Water Bunkering on Platforms

2009

Water Report 113

Safe, Sufficient and Good Potable Water Offshore A guideline to design and operation of offshore potable water systems 2nd edition Eyvind Andersen Bjørn E. Løfsgaard

Water Water Repo Report rt 113 113

Saf e, Suff uf f i ci cie ent and Good oo d Pota ot able bl e Wa Water Offsh Off shor ore e A guideline to design and a nd operation operatio n of offshore potable water systems nd

2 edtion Eyvind Andersen Bjørn E. Løfsgaard

Published by Norwegian Institute of Public Health Division of Environmental Medicine Department of Water Hygiene November 2009 Titel: Water Report 113 Safe, Sufficient and Good Potable Water Offshore A guideline to design and operation of offshore potable water systems nd

2 edition Au th or s: Eyvind Andersen Bjørn E. Løfsgaard Ordering: The report can be downloaded free of charge: www.fhi.no Design cover: Per Kristian Svendsen Cover photos: Bjørn Løfsgaard (left), Eyvind Andersen (right) ISBN: 978-82-8082-361-8

Sufficient, Safe and Good Potable Water Offshore

Preface The NIPH wants to express thanks for input to the guideline to: Torbjørn Andersen, John Øyvind Auestad, Anne Nilsen Figenschou, Joar Gangnes, Karl Olav Gjerstad, Kjersti Høgestøl, Eivind Iden, Synne Kleiven, Olav Langhelle, Kyrre Loen, Ola Nøst, Bjørn Pedersen, Einar Pettersen, Yvonne Putzig, Jan Risberg, Håkon Songedal Bjørn Steen and Kjetil Todnem. We offer special thanks to Catrine Ahlén and Yvonne Putzig who made the draft of the chapter on potable water systems on diving vessels; and to Sam Sutherland for valuable input to the English version.

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Preface to the 2 edition This guideline has been revised by Eyvind Andersen at the Norwegian Institute of Public Health (NIPH), Department of Water Hygiene. It was translated by Rigmor Paulsen (NIPH), with 2nd edition changes by Eyvind Andersen. If any discrepancies occur, the Norwegian version of the guideline takes precedence. We emphasise the following changes: The recommended testing programme in ap pendix 4 is revised. Colour analysis is recommended when bunkering. For the yearly analyses, sodium and chloride have been removed, and analysis of hydrocarbons, mineral oils have been added. Some offshore units will also have to analyse glycols. Chapter 6.1.1 describes routines for operating and documenting electro chlorination of sea chests. Chapter 8.3 on UV-disinfection is revised. This both to emphasise that UV-units that are approved according to the old type approval standard should be phased out, and to emphasise which water quality the units must be able to handle. The system design example in chapter 5.1 has been changed with regard to tank design, control of water flow and safeguarding against contamination. Section 9.1.4 and appendices 1 and 13 contain new information regarding tank coating. A new section 9.2.5 on protection against pollution of the distribution system A new section 9.2.7 on legionella prevention, based on contents from the previous edition of this guideline, supplemented with information from the Norwegian legionella guideline. •

From the preface to the 1st edition Working with potable water brings you in contact with many special fields, such as environmental health protection, technical disciplines, law and medicine, just to mention a few. The different as pects are not equally and thoroughly explored in this guideline. Chapters 1 to 4 contain general information on regulations, system control requirements and water quality. The remaining chapters cover design, operation, and maintenance of various components of the potable water system.

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The objective with the guideline is: To inform about basic considerations to be taken in planning and construction of potable water systems offshore, without covering all technical details. To guide personnel in operation, control and maintenance of potable water systems offshore to ensure a safe potable water.

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The guideline gathers NIPH’s information to industry, state authorities and specialists in relevant fields. Within the offshore section it replaces the following guidelines: B3 Teknisk utforming av drikkevannsanlegg offshore B5 Desinfeksjon av drikkevann C5 Operation, control and maintenance of potable water systems offshore G2 Kvalitetsnormer for drikkevann •

The guideline is published on the NIPH offshore webpages: www.fhi.no/offshore, and will be updated regularly. Comments to the guideline can be sent to [email protected]

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Oslo, 2nd November 2009 Truls Krogh Department of Water Hygiene Division of Environmental Medicine Norwegian Institute of Public Health

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CONTENTS

PREFACE ..................................................................3

1.1 SUFFICIENT, SAFE AND GOOD POTABLE WATER ................................................................................... 6 1.2 HOW TO USE THE GUIDELINE ............................ 6 1.2.1 GUIDELINE STATUS ........................................... 6 1.2.2 GUIDELINE APPLICATION .................................. 6 1.3 DEFINITIONS ....................................................... 7

4.3 QUALITY REQUIREMENTS ............................... 20 4.3.1 DAILY ANALYSES ........................................... 20 4.3.2 A NALYSES WHEN BUNKERING ........................ 21 4.3.3 MONTHLY ROUTINE CONTROL ....................... 22 4.3.4 EXTENDED YEARLY ROUTINE CONTROL ........ 24 4.3.5 PARAMETERS WITHOUT YEARLY ANALYSIS RECOMMENDATION ................................................. 25 4.4 DRINKING WATER IN BOTTLES OR OTHER PACKAGING ............................................................ 26 4.5 ESSENTIAL ANALYSIS EQUIPMENT .................. 26

2. REGULATIONS AND AUTHORITIES ............8

5. GENERAL DESIGN REQUIREMENTS.........28

2.1 AUTHORITIES ..................................................... 8 2.2 REGULATIONS .................................................... 8 2.2.1 THE POTABLE WATER R EGULATIONS .............. 8 2.2.2 HEALTH, E NVIRONMENT AND SAFETY R EGULATIONS (HSE) ................................................ 9 2.2.3 R EGULATIONS CONCERNING POTABLE WATER

5.1 DESIGN EXAMPLE ............................................. 28 5.2 DIRECTIONS FOR DESIGN AND CONSTRUCTION OF A POTABLE WATER SYSTEM ............................. 30 5.2.1 ERGONOMIC DESIGN ....................................... 30 5.2.2 SAFEGUARDING AGAINST MISTAKES .............. 31 5.2.3 STORAGE CAPACITY REQUIREMENTS ............. 31 5.2.4 HYGIENIC BARRIERS – PREVENTING CONTAMINATION ..................................................... 31 5.2.5 PLACING, MARKING AND PROTECTING THE EQUIPMENT .............................................................. 32 5.2.6 LOCATION OF SAMPLE POINTS ........................ 32 5.2.7 PAINTS AND PROTECTIVE COATINGS .............. 32 5.3 ALTERATIONS OF THE POTABLE WATER SYSTEM ................................................................... 32

1 INTRODUCTION..................................................6

SYSTEM AND POTABLE WATER SUPPLY ON MOBILE OFFSHORE UNITS ...................................................... 10

2.2.4 THE LAW ON FOOD ......................................... 10 2.3 NORWEGIAN INSTITUTE OF PUBLIC HEALTH FUNCTIONS .............................................................. 10 2.3.1 EVALUATION OF NEW OFFSHORE UNITS ......... 10 2.3.2 AUDITS............................................................ 10 2.3.3 EVALUATION OF POTABLE WATER REPORTS ..10 2.3.4 PRODUCT APPROVAL ...................................... 11

6. POTABLE WATER PRODUCTION ...............33 3. MANAGEMENT SYSTEMS .............................12

6.1 SEA WATER INLETS .......................................... 33 6.1.1 POSSIBLE POLLUTION THREATS ...................... 33 6.1.2 PLACING SEA WATER INLETS .......................... 33 6.2 EVAPORATION .................................................. 34 6.3 REVERSE OSMOSIS ........................................... 35 6.4 CONDUCTIVITY CONTROL ............................... 36 6.5 USE OF CHEMICALS .......................................... 36

3.1 POTABLE WATER DOCUMENTATION ............... 12 3.2 COMPETENCE ................................................... 12 3.3 MAINTENANCE SYSTEM ................................... 12 3.4 COLLECTION , PROCESSING AND USE OF DATA 13 3.5 HANDLING OF NON -CONFORMITIES ................ 13 3.6 EMERGENCY PREPAREDNESS .......................... 14 3.7 SYSTEM AUDITS ................................................ 14 3.8 REPORTING TO THE AUTHORITIES AND APPLICATION FOR EXEMPTIONS ........................... 14

7 BUNKERING POTABLE WATER ...................37 7.1 DESIGN OF BUNKERING SYSTEM , INCLUDING WATER CIRCULATION ............................................ 37 7.2 DISINFECTION REQUIREMENTS ....................... 39 7.2.1 FLOWMETER REGULATED DOSING ................. 39 7.2.2 DOSING WITH A MANUALLY REGULATED PUMP ................................................................................. 39 7.3 BUNKERING PROCEDURES ............................... 39 7.3.1 PRIOR TO BUNKERING..................................... 39 7.3.2 BUNKERING .................................................... 39 7.3.3 AFTER BUNKERING ......................................... 40 7.4 LOGGING .......................................................... 40

4. WATER QUALITY ............................................15 4.1 POTABLE WATER AND HEALTH ....................... 15 4.1.1 MICROBES ....................................................... 15 4.1.2 CHEMICAL SUBSTANCES POSING HEALTH HAZARDS ................................................................. 16 4.2 OTHER GENERAL REQUIREMENTS .............. 17 4.2.1 SMELL AND TASTE .......................................... 17 4.2.2 DISCOLOURED AND TURBID WATER ............... 17 4.2.3 CORROSIVE WATER ......................................... 17 4.2.4 ITCHING AND SKIN IRRITATION ...................... 19 4.2.5 WATER TEMPERATURES ................................. 20

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APPENDICES APPENDIX 1 – CHECK LIST FOR DESIGN OF

8. WATER TREATMENT .....................................41 8.1 CORROSION CONTROL ..................................... 41 8.1.1 ALKALINE FILTER ........................................... 41 8.1.2 SODIUM SILICATE ........................................... 42 8.2 DISINFECTION BY CHLORINATION .................. 42 8.2.1 THE SIGNIFICANCE OF THE WATER QUALITY ..43 8.2.2 SODIUM HYPOCHLORITE ................................. 43 8.2.3 CALCIUM HYPOCHLORITE ............................... 44 8.2.4 DESIGN............................................................ 44 8.2.5 OPERATION AND MAINTENANCE .................... 45 8.3 DISINFECTION BY UV-RADIATION .................. 45 8.3.1 THE IMPORTANCE OF WATER QUALITY .......... 45 8.3.2 DESIGN, DIMENSIONS AND APPROVALS .......... 46 8.3.3 OPERATION AND MAINTENANCE .................... 47 8.4 ACTIVE CARBON FILTERS ................................ 48

POTABLE WATER SYSTEMS ON OFFSHORE UNITS

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APPENDIX 2 – CHECK LIST FOR OPERATIONAL DOCUMENTATION OF A POTABLE WATER SYSTEM

(POTABLE WATER MANUAL ) ................................. 64 APPENDIX 3 – EXAMPLE OF A DAILY POTABLE WATER LOGBOOK .................................................. 67 APPENDIX 4 – RECOMMENDED ANALYSIS PROGRAMME AND QUALITY REQUIREMENTS ...... 68 APPENDIX 5 – BUNKERING LOG ............................ 70 APPENDIX 6 – RECOMMENDED REQUIREMENTS TO SUPPLY BASE AND VESSELS ................................... 71 APPENDIX 7 – INSTRUCTIONS FOR BACTERIOLOGICAL TESTING OF POTABLE WATER

................................................................................. 72 APPENDIX 8 – INSTRUCTIONS FOR PHYSIO CHEMICAL SAMPLING , INCLUDING ANNUAL ANALYSES ............................................................... 73 APPENDIX 9 – TROUBLESHOOTING GUIDE ........... 74 APPENDIX 10 – RECOMMENDED PROCEDURES FOR BUNKERING POTABLE WATER ............................... 78 APPENDIX 11 – CALCULATIONS IN CONNECTION WITH CHLORINATION ............................................ 79 APPENDIX 12 – CLEANING AND DISINFECTION OF A DISTRIBUTION SYSTEM .......................................... 81 APPENDIX 13 – CLEANING AND DISINFECTION OF POTABLE WATER TANKS ........................................ 82

9. STORAGE TANKS AND DISTRIBUTION SYSTEM ..................................................................49 9.1 POTABLE WATER TANKS .................................. 49 9.1.1 STORAGE CAPACITY ....................................... 49 9.1.2 DESIGN AND LOCATION .................................. 50 9.1.3 OPERATION AND MAINTENANCE .................... 51 9.1.4 SMELL- AND TASTE PROBLEMS DUE TO PROTECTIVE COATING ............................................. 52 9.2 WATER DISTRIBUTION SYSTEM ....................... 52 9.2.1 PRESSURIZING WITH HYDROPHORE UNITS OR DAY TANKS .............................................................. 53 9.2.2 PRESSURIZING WITH PUMPS ............................ 53 9.2.3 DESIGN OF WATER DISTRIBUTION SYSTEMS ... 53 9.2.4 HOT WATER SYSTEMS ..................................... 54 9.2.5 PROTECTION AGAINST POLLUTION ................. 54 9.2.6 OPERATION AND MAINTENANCE .................... 55 9.2.7 LEGIONELLA PREVENTION .............................. 56 10. WATER SUPPLY ON DIVING VESSELS – SPECIAL REQUIREMENTS................................57 10.1 WATER ANALYSES .......................................... 57 10.2 WATER PRODUCTION ..................................... 57 10.3 DESIGN ............................................................ 58 10.4 MAINTENANCE ............................................... 58

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1 Introductio n

1.1 Suff ici ent, safe and g ood pot able water

1.2.1 Guideline status The Potable Water Regulations, see 2.2, define the requirements that must be followed during design and operation of potable water systems offshore. This guideline is prepared by the NIPH, and contains our best advice, based on the regulation requirements and on our experience from offshore inspections, research and reports from the offshore industry etc.

The purpose of the Potable Water Regulations is to ensure delivery of sufficient, safe and good potable water. The general philosophy is that, when good water sources are chosen, the water works treatment plant is optimal, and the routines for operation, control and maintenance are the very best, the result is good potable water. If one level fails, the safety is reduced.

The Norwegian offshore HSE-Regulations refer to our guideline when it comes to building and operating potable water systems on offshore units. Our advice will therefore be a key element in defining necessary safety requirements, regardless of whether one chooses the suggested solutions or not, see 2.2.2.

The quality requirements are defined in the Pota ble Water Regulations §12, and apply o all Norwegian potable water supplies: ”Potable water shall be hygienically safe, clear and without any specific smell, taste or colour. It shall not contain physical, chemical nor biological components that can lead to any health hazard in common use”. §14 in the Regulations require at least two hygienic barriers against all physical, chemical and microbiological pollution that could possibly affect the potable water supply. Two different safety barriers ensure that the potable water remains safe, even if one barrier fails periodically, due to human or technical failure.

In the guideline we have tried to only state the Regulations requirements. In addition we give advice on good practise, where the Regulations allow for use of various solutions. If the guideline states requirements that appear not to be defined in the Regulations, we would appreciate being informed of this. Therefore, examples on solutions and attached check lists must not be interpreted as absolute requirements. The companies must use their own judgement in deciding the need for equipment, operation routines and supervision in their specific activity.

Different skilled groups co-operate to run potable water systems offshore. To avoid problems and misunderstandings, it is important that these groups “talk the same language” and have access to relevant information. Failure in an offshore potable water system is normally caused by human errors or inadequate operation systems. Only rarely is technical failure the cause of serious problems. Even the best systems can deliver bad water quality if operation systems are inferior, while a technically weaker system can deliver safe and good potable water when it is run by dedicated personnel. Internal control, including sufficient routines for training personnel and for operation of the system, is crucial to secure that the system functions adequately in the long run.

1.2.2 Guideline application The guideline, including appendices, can be used in different manners, depending on the various needs the user might have: •

1.2 How t o us e the guideli ne The guideline gathers the NIPH material for offshore potable water systems. The guideline can be used as a complete reference book, or to just get help to solve one single problem.

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Before planning water supply systems on new offshore units, those responsible should read the guideline, as this is necessary in order to secure the very best solutions. In the long run this will give the best results with regard to quality, operation and costs. Use of the design check list in appendix 1, and the check list for control systems in appendix 2, can not compensate for a thorough study of the guideline, but is meant to be used after the planning process, to ensure that solutions chosen are adequate. The guideline may be used as a reference book, to be consulted in the every day


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Operation analyses of potable water: Analyses taken of the potable water as an in-house control measure, and in adjusting the operation of the potable water system, including analyses performed when bunkering potable water.

operations, when relevant information is not available in the unit’s management system. The guideline may also be used in potable water courses for offshore personnel. Furthermore, the guideline can help supervisory personnel in finding sound solutions when interpreting regulations.

Potable water: All types of water, treated or untreated, designated for drinking, cooking or other household purposes, regardless of the origin of the water, and regardless of whether it is delivered through a distribution system, from supply vessels, from bottles or other packaging, see the Potable Water Regulations §3.

1.3 Defini tion s

Conformity Explanation (CE): Explanation from the Petroleum Safety Authority Norway on the technical condition of a mobile offshore unit. The applicant’s organization and control system is assessed and found to be in accordance with relevant requirements in the Norwegian Offshore Regulations.

Potable water systems offshore (figure 1.1): The system normally consists of the following elements: water sources, sea water inlet, water producing systems, bunkering stations, treatment units, water tanks, transport systems and operation routines. The potable water system also includes the water.

Control: Status verification pertaining to requirements. Hygienic barriers: Natural or man made physical or chemical hindrance, such as means of removing, render harmless or killing bacteria, viruses, parasites and the like, and/or dilute, break down, destroy or remove chemical and physical components to a level where the substances no longer represent any health hazard, see Potable Water Regulations §3.

Reactions: Measures by supervisory authorities towards an operation, when non-conformities from the Regulation requirements are revealed. Simple and extended routine control: Routine control analyses of potable water should be sent to an accredited laboratory ashore, and used to document that the operation of the potable water system has proven adequate, and also as an instrument for making operational improvements.

Hygienically safe potable water: Potable water that neither contains physical, chemical nor microbiological components posing neither short nor long term health hazards. Letter of Compliance (LOC): A document issued by the Norwegian Maritime Directorate, con-firming that a foreign registered offshore unit complies with all technical requirements specified by the Norwegian Maritime Directorate and its affiliated supervisory authorities. Microbes: Microorganisms such as bacteria, parasites, fungus and virus. Offshore unit: Installation and equipment for the petroleum activity, but not supply- and auxiliary vessels, nor petroleum bulk carriers, see Regulations § 4, of August 31, 2001 regarding health, environment and safety in the petroleum business.

Figure 1.1: Potable water system with evaporator, scale inhibitor tank, chlorine tank, alkalizing filter and UV-units (Photo: Eyvind Andersen)

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2. Regulations and authori ties

2.2 Regulations

Regulations and authorities concerning offshore potable water supply can, at first glance, seem complicated. There are several regulations and authorities to relate to. Previously Norway had one potable water regulation for water works ashore, and two different regulations for offshore units, depending on whether these were defined as mobile platforms or permanent units. The Regulations in force today are practically the same for the various units. Furthermore, the guidance and control functions for both types of units are conducted by the same specialists. Table 2.1 is a summary of existing Regulations and suggested standards.

Regulations of 4 December, 2001 concerning potable water, fully applies where special offshore provisions have not been given. Special provisions in the Regulations on Health, Environment and Safety within the petroleum business of August 31, 2001, apply to potable water as well. Those provisions apply to all units participating in the Norwegian offshore operations. In addition, Regulations of September 4, 1987, concerning potable water systems and potable water supply on mobile offshore units, apply to units that hold maritime certificates from The Norwegian Maritime Directorate. The law on Food Safety also applies offshore. Links to the above Regulations can be found on the NIPH offshore pages: www.fhi.no/offshore

2.1 Author ities The Petroleum Safety Authority Norway, The Norwegian Pollution Control Authority and The Norwegian Board of Health, or person/institution given supervisory authority by these organizations, assess whether offshore industry adhere to the requirements for health, environment and safety. The Petroleum Safety Authority coordinates the supervisory activities on the offshore units. The Norwegian Board of Health, represented by the subdivision in Rogaland County, is responsible for the supervision of health and hygiene matters. According to the new law on food, The Norwegian Food Safety Authority (Mattilsynet) is the legal authority, and that law applies offshore as well. Until clarification on how this authority is going to be executed, the work continues as before. Some mobile offshore units have maritime certificates from the Norwegian Maritime Directorate (NMD). When units holding such certificates are engaged in Norwegian petroleum activities, these certificates may be used to document standard on health, environment and safety issues.

The assessment made by the NIPH, is that all offshore units operating on The Norwegian Continental Shelf, must comply with all rules and regulations mentioned above. This should not cause any problems since the different Regulations are not in conflict, but rather complement each other. In their specialized fields they jointly secure the ultimate goal, namely safe and good potable water in sufficient quantities, observing the following main points: •

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The Potable Water Regulations state requirements for water quality and analyses. The Health, Environment and Safety Regulations pose general requirements for design and operation of a potable water system on offshore units, and also refer to: Regulations concerning potable water systems and potable water supply on mobile offshore units, and the NIPH guideline, which together give requirements and advice on design and operation of potable water systems offshore.

2.2.1 The Potable Water Regulations The Potable Water Regulations of December 4, 2001 is in accordance with the European Union Regulations for potable water. The Regulations apply to units operating on the Norwegian continental shelf, but it does not emphasize the special requirements necessary to obtain good quality potable water offshore. § 2 emphasizes that the Potable Water Regulations yield to special

The NIPH has no formal authority regarding potable water offshore, but the Norwegian Board of Health and the NMD have assigned the task of advising on the potable water systems on their behalf, to the NIPH. Formal reactions and recommendations are issued by the two departments based on the NIPH findings and suggestions. 8


Table 2.1: Regulations and suggested standards for offshore units on the Norwegian continental shelf Permanent units Mobile units registered Mobile units registered in the Norwegian ship in foreign ship registers. register and foreign Bound to conformity units with LOC* explanation. (CE)* The Law on Food Legally binding Potable Water Regulations Legally binding Health, Environment and Legally binding Safety Regulations Regulations concerning potable water system and Suggested Legally binding Suggested standard** potable water supply on standard** mobile offshore units The NIPH – Guideline Suggested standard**

NORSOK P-100 system 53 Suggested standard** * see 1.3 ** see HSE Framework Regulations § 18, Facilities Regulations § 62 and Activity Regulations § 11 regulations for potable water offshore. There are no such special regulations for potable water quality and requirements for analyses. Within these fields the requirements of the Potable Water Regulations have to be followed. The NIPH, in agreement with The Norwegian Board of Health, has given an analyses programme for potable water on offshore units, see 4.3, and recommends the use of this specific programme. The programme has been revised as suggested by The Norwegian Food Safety Authority, and designed to accommodate the requirements of the Potable Water Regulations.

be proven to be at least as reliable. The complete Health, Environment and Safety Regulations cover potable water, but not all of it is equally relevant. The most important points are: •

2.2.2 Health, Environment and Safety Regulations (HSE) For offshore units on the Norwegian continental shelf, the Regulations of August 31, 2001 apply. The HSE Regulations consist of five regulations, the Framework Regulations with detailed regulations on operations, information requirements, units and activities. Potable water systems offshore differs in many ways from onshore systems, and the HSE Regulations yield the right to apply relevant requirements that is not necessarily evident in the Potable Water Regulations.

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The HSE Regulations give general requirements as to function, and thus contain no details for design and operation. But, in the comments to the Regulations, standards are specified. According to the Framework Regulations § 18 these standards are binding, meaning that the standards are to be followed, or the alternative solutions chosen must 9

The Framework Regulations are the basis for the health, environment and safety work. The object clause requires health, environment and safety levels to be the very best and maintained by systematic work and constant improvement. Chapter III gives the basic principles to be as follows: All health, environment and safety matters should be adequately taken care of and hazards reduced to a minimum. Organization and level of competence should be satisfactory and according to requirements. The Management Regulations pose important requirements to the design process such as hazard reduction, barriers, planning and analysis. The Facilities Regulations pose general requirements to design and equipment, such as top level security, ergonomics and uncomplicated and sturdy design. § 62 establish that the design should be in accordance with requirements in the Activities Regulations and the Potable Water Regulations. Specific design requirements are not defined. Comments to this paragraph state that, if the requirements for mobile offshore units are fulfilled, so will the requirements in the Facilities Regulations be. The Regulations requirements can also be fulfilled by following the requirements in the


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NORSOK-standard no. P100 supplied with the guideline issued by the NIPH. The Activities Regulations cover performance of activities on the unit. § 11 states that sufficient supply of good quality potable water is required, and reference is made to the Potable Water Regulation. In comments to § 11 it is stated that offshore units that fulfil the requirements for mobile offshore units, normally will fulfil the Activity Regulations requirements. Reference is also made to the guideline pre pared by the NIPH.

2.3 Norwegian Instit ute of Publi c Health - functi ons The NIPH advice the Norwegian Board of Health and the Norwegian Maritime Directorate on matters related to potable water and potable water systems on offshore units. NIPH also provides general advice within this special field. In addition to general guidance to the offshore industry, the institute is engaged in the following:

2.3.1 Evaluation of new offshore units NIPH evaluates the potable water system on new builds according to regulations (table 2.1). To avoid unnecessary and costly mistakes in the construction process, it is advisable to consult the institute as early as possible in the concept phase and stay in contact throughout the construction period. NIPH suggests that the project manager uses our check list in appendix 1, to be more certain that the project is according to standard.

For both design and operation of potable water systems, the Regulations for mobile offshore units, is a recommended standard. By using it, the HSE Regulations requirements are normally covered. If other solutions are chosen, it must be documented that these solutions are equally good. Reference is also made to the guideline issued by the NIPH, but the guideline is in general in coherence with the Regulations for mobile offshore units. However, some elements are more clearly and thoroughly defined in the NIPH guideline.

When the project is near completion, a final survey is made of the unit at the yard. If standards have been followed, the NIPH normally has few objections, and the supervisory control authorities can be notified that there are no objections to start-up of the unit. Generally a new inspection is made after one year of operation, to ascertain the system is functioning properly.

2.2.3 Regulations concerning potable water system and potable water supply on mobile offshore units The Norwegian Maritime Directorate issues certificates for Norwegian mobile units. The Regulations of 4 September 1987 concerning potable water systems and potable water supply on mobile offshore units have stringent requirements that must be met in design and operation of potable water systems. These Regulations also refer to the Potable Water Regulations.

2.3.2 Audits Audits are carried out based on risk and vulnerability analyses. Relevant system documentation is compared with the Regulations requirements. It is emphasized that internal control systems find and solve problems, and that similar problems are prevented from occurring in the future.

It is the license owner’s responsibility to document that the mobile offshore units on the Norwegian Continental Shelf comply with the requirements of the HSE Regulations. A certificate from the Norwegian Maritime Directorate normally assures this with respect to potable water.

2.3.3 Evaluation of potable water reports According to Framework Regulations § 17 and Potable Water Regulation § 7, the license owner is asked to submit potable water reports to the authorities, represented by NIPH. This enables the institute to catch problems with-out actual on-site surveys. Potable water reports include results of analyses made by accredited laboratories. In case of deviations from requirements, information should be given as to corrective measures taken. If events important to the safety and quality of the portable water systems occur, this should also be reported.

2.2.4 The Law on Food The law on food production and food safety of December 19, 2003, applies to potable water systems and potable water supply on mobile offshore units as well, see 2.1.

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include alkaline filter material, corrosion- and scale inhibitor in heating circuits, cleaning products, disinfection products, anti freeze products, etc. Such products are to be used only in accordance with the dosing requirements for that specific product. It is the producer that usually applies for NIPH approval.

2.3.4 Product approval Paint and protective coatings can pollute the potable water, see 9.1.4. To prevent pollution, the NIPH type-approved products should be used in offshore potable water systems. The NIPH also approve water treatment products and products that may pollute the potable water through leakages or after system maintenance. NIPH approval is not necessary for water pipes in metal alloys or hard plastic, or for gaskets and hoses etc., as long as these products have been produced for potable water use by an acknowledged manufacturer. The Norwegian Maritime Directorate requires the use of “certified” products, and the NIPH typeapproval is such a “certification”. Products that have HSE data sheets are not necessarily approved for potable water use by our institute.

Type-approval of UV-units is given by the NIPH to ensure that the unit carries sufficient radiation capacity. The units are therefore approved based on requirements such as maximum water supply, worst case water quality and necessary maintenance. If these requirements are not followed, the result is a sense of false security. UV-unit requirements are described under 8.3.2. Lists of type-approved water treatment products, protective coating/paints and UV-units, can be found on the NIPH net pages: www.fhi.no/offshore

When type-approved products are used in accordance with approval requirements and the supplier’s recommendations, they are considered safe. Approved products for potable water treatment

Figure 2.1: Picture taken at the shipyard of the Skarv unit (Photo: Eyvind Andersen)

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3. Management systems The Framework Regulations § 13 determine that “The party responsible shall ensure that analyses are carried out, which will provide the necessary decision basis in order to give due consideration to health, environment and safety”. The management system for potable water is part of this, and must be adjusted to the various units and organizations. The party responsible shall ensure that the management system functions properly by, for example, conducting system audits.

But, even if the format of the documentation is not of the greatest importance, there are numerous conditions that require documentation. Appendix 2 lists the type of information that ought to be included in the potable water document as a minimum. This documentation must be organized in a manner that makes is easy to find and compile.

3.2 Competence The Framework Regulations § 10 establish that ”The party responsible shall ensure that everyone carrying out work for him in petroleum activities, have the competence required to carry out such work in a safe and prudent manner”.

The established level of management of health, environment and safety should be under frequent assessment. The management system should be continuously improved as a natural consequence of operation experiences, changes in the Regulations, system revisions etc. This will improve the quality of potable water supply. The management system is based on internal control, with emergency preparedness considerations being an integrated part of the system. The following main points must be included:

The party responsible decides the degree of training needed for personnel within the different disciplines, including routines to maintain and refresh this knowledge. Training should be carried out before personnel are assigned to their tasks. The party responsible must have routines to ensure and document that the necessary training has been given. This documentation could be a job description and specifications for the various tasks, including potable water education program. There are several institutions offering courses in offshore potable water treatment. The party responsible may also choose to take responsibility for the training, but is then required to document that this training is on a satisfactory professional level.

3.1 Potable water doc umentatio n The Framework Regulations § 17 establish that “Material and information which is necessary to ensure and to document that the petroleum activities are planned and carried out in a safe and prudent manner shall be prepared and retained”. For potable water systems it is common to prepare a manual that covers the main documentation requirements mentioned here.

3.3 Maintenance system

Potable water manuals are often voluminous documents containing most of the information needed to run the system, but there are smaller manuals which referer to other documents, procedures and systems with more detailed information. The current trend is that more and more of the potable water documentation is integrated in company data systems and/or unit documentation systems.

Many components in an offshore potable water system require regular maintenance in order to function properly at all times. Frequency and the extent of the maintenance are in part based on requirements made by the authorities, for example the yearly cleaning and disinfection of tanks and pipe systems (figure 3.1). Other requirements follow the general requirements in the Activity Regulations, chapter IX. §43 state that “the unit system and equipment is to be classified in accordance with the health, environment and safety consequences of a potential malfunction”. The classification is the basis for choosing the type of mainte-

Both methods can function well. The important point is that the information is actually used and is easy to up-date whenever the need arises, and that it is easy to find relevant information both in the daily operation and when problems arise.

12


nance activity, frequency and priority of the various maintenance activities”.

3.4 Collecti on, proc essing and use of data The Management Regulations § 18 require that the party responsible collects and processes data information for:

A planned maintenance programme must be pre pared, describing the extent and frequency of the maintenance work on the potable water system, including evaporator, reverse osmosis unit, alkalization filter, bunkering station, chlorination plant, potable water tanks, UV-unit, measuring instruments, non-return valves, active carbon filter, pressure setting systems and pipe system. The supplier of the equipment should document the necessary maintenance.

•

• •

Surveillance and control of the state of technical, operational and organizational conditions Providing statistics and design data bases Implementing corrective and preventive measures

In connection with potable water systems, focus is mostly on the water analyses. This is obviously important, but even more important is the collection of data on critical operational parameters, see specifications for hygienic barriers under 5.2.4, and work carried out on the potable water system. Exchange of such information is necessary at the time of shift handovers, and acts as an important source for detecting faults at the earliest opportunity, whereas water analyses uncover problems later, see 4.3.

A job description has to be provided for each element in the maintenance system. Such a description should present all necessary safety measures and description of how the work is to be done and by whom.

The party responsible chooses type of data collection and routines are to be used. Suggestions for logging the daily potable water analyses are illustrated in appendix 3, and such logging must be supplemented by logging of bunkering, maintenance and other operations.

3.5 Handlin g of non-conformi ties The Management Regulations § 20 establishes that “the party responsible shall record and follow up non-conformities requirements to health, environment and safety legislation”. Included are also non-conformities to internal requirements that are of significance in fulfilling the requirements contained in the HSE Regulations. Non-conformities ”shall be corrected, their causes established and corrective actions taken to prevent recurrence of the non-conformity. The actions shall be followed up and their effect shall be evaluated”.

Figure 3.1: Demand for cleaning of tanks at least once a year is set to avoid situations illustrated in the picture above, where there is a layer of mud at the bottom of the tank. Such occurrences have to be handled as a non-conformity case. (Photo: Bjørn Løfsgaard)

The NIPH has found that deviations to the requirements for potable water systems are often not being followed by such non-conformity actions. Inferior water quality and failure in the production are frequently not considered a serious ”unwanted 13


occurrence” requiring non-conformity actions. The majority of owners have to improve the potable water management systems in this regard. It is also necessary to establish norms for operation and water quality that may require nonconformity actions.

3.7 System audit s § 10 in the Framework Regulations state that “The operator shall have an organization in Norway, which, on an independent basis, is capable of ensuring that petroleum activities are carried out according to rules and regulations”. In other words, the operator shall have an organization competent enough to verify that control systems are functioning in accordance with requirements. Established internal audit systems, both on the unit and by personnel from the onshore organization, are important tools in this work, and the necessary procedures, check lists etc. for such work should be established.

3.6 Emergency preparedness Failure within a basic function such as the potable water system is very serious. The Activities Regulations § 64 state that the operator or the one res ponsible for the operation of a facility shall pre pare a strategy for emergency preparedness against situations of hazard and accidents. This shall be established on the basis of results from risk- and vulnerability analyses as mentioned in the Management Regulations, and should at least include the following scenarios: • •

•

•

3.8 Repor tin g to th e author iti es and application for exemptio ns The Potable Water Regulations require reports to the supervisory authorities. The results from monthly and yearly water sampling are normally included in the half-yearly or yearly report, sent to the NIPH, who assesses the report on behalf of the Norwegian Board of Health and the NMD.

Outbreaks of water borne epidemics Chemical pollution of the potable water causing it to be unsuitable for use, for example as a consequence of bunkered substandard water, leakage or faulty connections to various systems. Lack of water due to leakage, technical failure, bad weather or other causes Malfunction in the disinfection process or other circumstances causing hazards to the quality of the potable water.

For most of the parameters the duty to report is complied with when correcting measures of minor non-conformities are documented in such reports. The reports should describe deviations, presumed causes and corrective measures taken. Findings of E. coli and intestinal enterococci must be reported immediately, at the latest the first working day after discovery. The same applies to major nonconformities to the Potable Water Regulations, jeopardizing the water supply on the unit. If it is not possible to correct non-conformities quickly, the company must apply for exemptions according to the Framework regulations section 59, see also the enclosures to the potable water regulations, covering dispensations.

Based on the emergency preparedness analyses being done, an emergency preparedness plan should be established for each unit. The emergency preparedness strategy is meant to prevent hazardous situations from arising, and to establish routines for actions to be taken.

14


4. Water quality Potable water is our most important nutrient, and is used for both drinking and cooking. The water being used for personal hygiene and all types of cleaning requires the same high quality (figure 4.1). It is therefore important to have enough water of satisfactory quality to cover all types of usage.

4.1.1 Microbes Potable water shall not contain microbes that can lead to disease. When suspecting an outbreak of a contagious disease, it is important to locate the source and eliminate it quickly, thereby preventing spreading. To be able to do this, it is necessary to have an emergency preparedness plan, see 3.6. Sufficient preventive safety measures are achieved only by building good potable water systems and having sufficient internal control.

Water treatment is described in chapter 8. It is important to establish sufficient hygienic barriers in order to secure high quality potable water, see 5.2.4.

All potable water for consumption offshore has to be disinfected, but even then, microbes can cause problems. This can be due to failure in the disinfection process, or contamination after the disinfection process. Humans and animals have several means of defence against infectious disease. Whether infection will occur or not, depends on the power of the infectant and how much infected water that was consumed.

4.1 Potabl e water and health

Safe potable water secures good health, but water can also contain hazardous elements that can be divided into two groups: 1. Microbes that cause infectious disease or food poisoning, such as bacteria, virus and parasites. 2. Organic and non organic substances that may cause health hazards, such as acutely poisonous substances, substances that by accumulation in the human organism causing health hazards, carcinogenic and/or allergenic substances.

Infectious diseases are the most serious threats to the health, related to potable water supply. Faecal contamination from humans and animals is normally the cause of such infections, and human faeces are particularly dangerous. The most common water related infectious diseases are cholera, bacterial dysentery, salmonellosis, typhoid fever and hepatitis A. Lately, focus has been on bacteria like Yersinia enterocolitica and Campylobacter jejuni, viruses such as Norovirus (earlier called Norwalk virus), and protozoa like Giardia intestinalis and Cryptosporidium parvum. Infections by these bacteria and parasites cause diarrhoea with strong abdominal pain. Recently attention has been drawn to the dangers caused by the Legionella pneumophila causes, see 9.2.7. It is established that the different types of epidemics descry bed in Norway are most often set off by several unfortunate circumstances. The offshore units are as susceptible to human and technical malfunctions as is the case onshore, and there are reasons to be on guard.

Indirect health hazards have to be considered as well. It can, for example, be difficult to obtain a satisfactory disinfection by chlorine or UV-radiation if the water is discoloured or holds a large quantity of particles, see 4.2.2.

Since the potable water is used in cooking, micro bes in the water can cause food borne infections as well. Some disease producing bacteria can grow in food products, and just a few bacteria can, within a short time, grow to huge concentrations and make consumers ill. Some of the bacteria in food

Figure 4.1: Potable water is our most important nutrient, and must be treated effectively in order to secure safe delivery (Photo: Lasse Farstad)

15


produce toxic substances that can cause poisoning even if the food is properly cooked and the bacteria killed in the cooking process.

potentially hazardous substances should be as low as possible. Offshore, such exposure may be a result of contaminated seawater supply or unfortunate occurrences in the operation of the unit system, for example back-suction through hose connections. It is important to minimize the risk of pollution related to materials and additives that come in contact with the potable water during transportation, storage, treatment, leakage etc. See certification requirements in 2.3.4.

To analyse potable water for every type of infectious substances that might transmit a disease is very demanding, and is not done. Instead, analyses are done on various types of indicator organisms such as microbes prevalent in large amounts in faeces from humans and animals, and having at least the same life span as the true infectious substances (figure 4.2). The group ”coliform bacteria” is being used as an indicator for faecal contamination, and the bacteria E. coli indicates fresh faeces. When an indicator organism is found in the water, it is a sign that there might be disease producing organisms in that same water.

Chemically caused health problems are seldom connected to acute poisoning by hazardous substances, but more often a result of prolonged ex posure to small amounts of those substances, finally resulting in health problems. Most significant are substances accumulating in the organism, causing cancer or triggering allergic reactions. When the human body is exposed to, for instance, heavy metals over a period of time, the accumulation may reach a critical level, resulting in illness. Limit values for such substances are set to a maximum acceptable daily intake, with sufficient safety limits to avoid levels hazardous to the health in the course of a lifetime.

The parameter ”Colony count 22o C” is used to assess the level of biofilm in the pipe system. Consequently the “Colony count” may also indicate growth in the pipe system of organisms hazardous to the health, but not detected by other indicator parameters. With a colony count below 100 per ml there is little risk of harmful exposure to such organisms. In a well maintained and operated system it is often possible to achieve colony counts below 10/ml.

Some chemical substances are classified as carcinogenic, and many of these are genotoxic. For such substances there is no threshold value for when damage may occur, and these substances are not supposed to exist in potable water. Since it is im possible to avoid traces of such substances in the water, Norway has set the upper limit value, based on acceptable life time risk, to be lower than 10 -6. This means that fewer than one out of a million people drinking two litres of water containing maximum acceptable amount of this substance every day for 70 years, develop cancer. Even so, the chance of developing cancer will be signifycantly lower, since limits are set with a high safety margin, and detected concentrations of the substances only rarely are close to the limit values. The danger is further reduced by the fact that a person seldom drinks water from the same source during his or her entire lifetime.

Figure 4.2: Birds regularly rest on offshore plat forms, and some even nest there. They can spread pathogens for example through insufficiently secured air vents and bunkering pipes. (Photo: Bjørn Løfsgaard)

Disinfection is crucial in safeguarding the potable water, but some disinfection methods may cause hazardous by-products. The chlorine doses used in Norway do not cause any direct health hazards, but there may be a possibility that the process can form chlorination by-products causing health haz-

4.1.2 Chemical substances posing health hazards Potable water shall not contain chemical substances that may pose a threat to health. Exposure to 16


ards. We cannot draw a final conclusion yet, but for this process to take place, it is a prerequisite that the water contains organic substances such as natural organic material, see 4.2.2. Potable water produced offshore seldom contains such material. Some units that evaporate water, where electro chlorination is used as marine growth prevention in the sea chests, have found chlorination by-products in the produced water. If the potable water is bunkered onshore and has a low colour value (under 20 mg Pt/l), and is chlorinated with the low chlorine levels used in Norway, it is safe to assume that the chlorination by-products will be insignificant, unless for some reason the water has increased levels of by-products prior to bunkering.

4.2

Even traces of chemicals like phenols, diesel and mineral oils can cause unacceptable smell and taste. A common reason for this in offshore pota ble water systems is the use of protective coatings that are applied too thickly or are not adequately hardened, see 9.1.4. High concentrations of for instance chloride and sulphate from sea water pollution can give potable water a salty taste. Corrosion particles, like iron, zinc and copper, can also cause an unpleasant taste to the potable water. How to remove the unpleasant smell and taste in potable water is covered in chapter 8.

4.2.2 Discoloured and turbid water Particles in water (turbidity) can encapsulate microbes that consequently will not be killed by UV or chlorination. Such particles and certain dissolved substances (for example humic particles), can absorb UV-light and reduce the effect of the UVtreatment, see 8.3. A high content of organic material will also result in high chlorine consumption that is not desirable, as it will cause unpleasant taste, see 4.2.1. Specific micro- organisms living in the pipe system (biofilm) feed on organic substances. Some of these may pose a health hazard, for example Legionella pneumophila which can cause Legionnaire’s disease, see 9.2.7.

Other general requirements

The potable water quality has to be satisfactory. According to the Potable Water Regulations the potable water shall be clear, without smell, taste and colour, and non-corrosive.

4.2.1 Smell and taste The potable water shall have no specific smell or taste, as unpleasant smell and/or taste can be a sign of other types of water pollutants. Investigation is then required in order to find the cause and initiate corrective measures. Potable water with a bad smell and/or taste may also lead to the crew drinking beverages less favourable to their health.

Potable water produced offshore normally contains few particles. The turbidity limit of < 1.0 FNU is generally easy to maintain. In corroded pipes, rust particles may loosen from the inside of the pipes and be transferred through the pipe lines to the consumer. Particles may also occur if there is bacterial growth in the system that loosens due to pH-changes or turbulent weather. Bunkered water may have a rather high content of particles, depending on the quality of the onshore water source. Particle contents will often have seasonal variations. Water delivered by supply vessels or water works onshore with visible turbidity should be refused. Problems with turbidity can be prevented by using particle filters, see 8.3.1.

Potable water with unpleasant smell and taste can originate both on the unit and outside. Such problems increase when the water temperature is high. If tanks and pipes contain organic material resulting in growth of micro-organisms, decomposing processes may give “rotten” smell and taste. A high content of humic particles can give a “marshy taste”. The chemical reaction between chlorine and nitric components may form new chemical combinations with strong smell and taste. Different microorganisms can be found in large amounts in sea water, and can release smell and taste components that may pass the water production units. Algae can also produce organic substances that do not smell, but form unpleasant smelling substances in contact with chlorine or UV-radiation. The same might happen when the water contains other types of organic substances.

Some water works onshore have surface water sources with visible yellow-brown colour from humic particles. Water from such water works should not be accepted for bunkering.

4.2.3 Corrosive water Corrosive water means water that corrodes the pipe line system, fittings and other installations 17


connected to the pipe line system. Untreated offshore produced water corrodes most metal surfaces that are not stainless steel or titan. Some corrosion will always occur in a potable water system, but it is important that the level is kept as low as possible, thereby avoiding inferior water quality, or that the entire system has to be replaced sooner than its normal life span would require. Corrosion may also lead to heavy metals, such as lead and cadmium, being released from the pipe line system and fittings, with undesirable consequences to health. By letting the water run for a short time before use, the heavy metal residue is lowered. Corrosion also necessitates more frequent cleaning and flushing of pipe systems, causing increase in operation costs.

Water from Norwegian water works is usually surface water and is commonly acid, with low levels of salt, calcium and alkalinity. Such water will corrode most materials. Potable water produced offshore is even more acid, has lower levels of calcium, alkalinity and, if produced by the reverse osmosis method, can have a relatively high salt level. Such potable water needs treatment, see 8.1. Pipe systems with speckled deposits on the metal surface may experience pitting corrosion. Under this residue the oxygen level will be lower due to the micro-organisms’ oxygen consumption. The difference will make electrons move from areas with residue to areas without such build -ups. This process releases metal ions to the potable water under the speckled residue, creating a pit in the metal. It is mainly a problem in iron and copper pipes, and offshore units based on bunkered water that are more susceptible to pitting.

Corrosion is due to a complex relation between pH-value, carbon dioxide content, oxygen content, hardness, (standard mainly set by calcium and magnesium), alkalinity (acid neutralizing ability, most of the time as a result of hydrogen carbonate content) and temperature. High content of ions such as chloride and sulphate can also increase corrosion. When the pH-value is below 7, the water is considered acid and will corrode most metals. High pH-values (> 9.5) will also corrode certain metals. A pH of approximately 8 is recommended. High levels of iron or copper are water quality parameters indicating corrosion problems. Table 4.1 describes favourable water qualities related to corrosion of different metals.

Corrosion by-products may reduce the water flow and make the water turbid, see 4.2.2. In potable water pipes of iron and steel, corrosion clusters may be formed especially in older pipe systems. The clusters are formed by bacteria converting dissolved iron to solid corrosion clusters. The corrosion clusters are hollow and can be crushed when the force of the water flow and flow direction is changed, see figure 4.3. Iron and copper can cause other problems too:

Table 4.1: Corrosion of various materials is best prevented by keeping the potable water quality within the following values: Material Critical parameters Optimal values

Iron and steel *

Galvanized iron

Copper

pH Alkalinity Calcium Chloride Sulphate pH Alkalinity Chloride Sulphate pH Alkalinity Chloride Sulphate

7,0 – 8,5 0,6-1,0 mmol/l >15 mg/l Lowest possible Lowest possible >7,0 >0,6 mmol/l Lowest possible Lowest possible >8,0 1-2 mmol/l Lowest possible Lowest possible

* stainless steel does not corrode in normal water quality

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4.2.4 Itching and skin irritation Some people working offshore are bothered by itching and other skin irritation. This is often seen in relation to showering, especially if there is scepticism to the treatment methods of the potable water (chlorination, alkalizing, reverse osmosis, etc). It is often difficult to find the cause for such symptoms. These problems may vary from one person to another and from one place to another. Many components, water related or not (like dry air etc.), may cause the problems to occur. If the problems can be related to showering and nothing else, we have made a list of possible causes and remedies: •

Figure 4.3: Corrosion clusters can result in poor water quality and clogging of pipes (Photo: Eyvind Andersen) •

•

High iron content can give turbid and red to brown water. Fittings, sinks, bathtubs and toilets become rust coloured. Stagnant water may get an unwanted taste, and washing white clothing may result in brownish-red spots due to iron deposits. High copper content can cause bad taste. Consumers may experience stomach problems if concentrations are very high. High copper concentration can also cause discolouring of sanitary installations and hair.

•

•

•

If metal piping of good quality is used, and the potable water treated to be as non-corrosive as possible, the main installation components in the system will last the life span of the unit. Unfortunately, there have been cases where parts or sometimes entire distribution systems have had to be replaced due to corrosion. This is costly.

•

Potable water pipes can leak due to corrosion, and as they often are concealed in the walls, the damage by the water can become extensive before being discovered. Corrosion control is covered in chapter 8.1. •

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One important explanation to the problems is frequent showering, using soap that removes the natural fatty protection the skin has. There is also the possibility that people shower more often offshore than when being at home. To solve such problems it is advisable to avoid taking showers every day or do without soap every time. Use of body lotion after showering may reduce the problems. Some people have symptoms wintertime even if they do not shower often. This is pro bably a cold weather eczema caused by the skin’s protective layer being washed off. Use of body lotion often reduces such problems. It has proven helpful for people experiencing itching and irritation of the skin to instead use a milder type of soap or shower oil. Even if the potable water in itself is not the cause of these skin problems, there are some micro-organisms existing in pipe systems that may set free substances sensitive persons react to. Disinfection of the cold and the hot water systems once a year can prevent growth of these micro-organisms. Hard water will also have an influence on how the skin might feel after showering. Taking showers in soft water makes the skin feel less dry but soapy, while showering in hard water makes the skin feel dry and coarse. Persons used to hard water will react to the soft water and the other way around. In Norway most waters are originally soft, but alkalizing/hardening makes the potable water harder, see 4.2.3. Treatment methods used offshore are not known to be the cause of itching or other skin reactions under normal circumstances.


Correctly administered chlorination and alkalization do not result in skin disorders.

water works owner can document that limit values are unlikely to be exceeded. In many aspects offshore water works differ from water works onshore, for example by producing potable water from sea water. Bunkered water comes from onshore water works with approved control routines. Some pollutants are thereby avoided in the offshore systems, but special conditions offshore make units suscepti ble to other types of pollution. The NIPH, in agreement with the Norwegian Board of Health and the Norwegian Food Authority, has suggested an analysis program for offshore potable water that covers the requirements in the Potable Water Regulations, see appendix 4. The Norwegian Board of Health suggests that the program is followed until 2014, when an evaluation of the number of parameters to be analysed will be made. The program must be supplemented with other parameters when contamination is suspectted.

4.2.5 Water temperatures The cold water temperature should be kept below 20o C to avoid growth of unwanted microorganisms. Cold water tastes better than lukewarm water, and the water should therefore be kept as cool as possible, see 4.2.1. By keeping fresh and cool water available, for example in water fountains connected to the potable water system, chances are that the platform crew will prefer water to the more expensive and less healthy alternatives. The hot water temperature must be kept high enough to avoid growth of unwanted microbes such as Legionella pneumophila, see 9.2.7.

4.3 Quality requir ements It is a common misunderstanding that the water analyses assure good quality potable water. Only high quality technical systems and adequate internal control can assure this. Water analyses will only afterwards document whether the water was of good quality or not. By revealing technical failure and insufficient internal control early, the analyses are still an important tool in securing and maintaining good quality potable water.

Limit values and the consequences of exceeding such parameters are commented on below. When the limits are exceeded, steps to find the causes have to be taken, and normal water quality restored. The authorities must be informed, and for problems that will last for some time, the company must apply for exemptions, see 3.8.

The Potable Water Regulations list several parameters to be analysed, thus documenting that the water quality meets the requirements. Some limit values are established because exceeding those values can cause short or long term health hazards, or because exceeding the limit value may make the potable water quality unfit for consumption. Exceeding other limit values do not pose any immediate health hazard, but may indicate that the potable water contains other components hazardous to health. Exceeding limit values may reveal that the water works is operated incorrectly and consequently may not produce safe potable water.

4.3.1 Daily analyses The potable water quality on board must be measured and logged daily, see appendix 3. Results are used to evaluate the need for adjustments of the potable water operations. The following parameters are included in the daily control: Smell: Should

not be noticeable. Smell may be a sign of contamination by, for instance chlorine/ chlorination by-products, volatile substances produced by algae, miscellaneous chemicals, oil, hydrogen sulphide gases (rotten smell), metals, salts, humic substances, marsh etc. A slight smell of chlorine is normal following the chlorination procedure. See chapter 4.2.1.

The potable water Regulations applies offshore and contains a total of 58 parameters to be measured. Apart from parameters applying to bottled water only, all the parameters should be measured at least once a year and many once every month or more often. The authorities can deviate from this programme provided that the

Taste: Should

not be noticeable. Unpleasant taste may indicate several types of contamination. See the above information regarding smell.

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Appearance : The water should be clear and without discolouring. This must be evaluated by using strong light and a white ore black background, depending on particle colour. Unclear water may indicate contamination and may even reduce the effects of disinfection, see 4.2.2.

free chlorine is not required, and consequently daily chlorine analyses are not necessary. Free chlorine values should be between 0.05 and 0.5 milligram per litre (equals ppm, parts per million). The NIPH recommends that the chlorine value is kept above 0.1 mg/l, as lower levels may be difficult to detect by the measuring methods used offshore. If free chlorine is not found, the disinfection methods have failed. It is then important to immediately establish procedures to avoid infections and prevent such situations to develop in the future.

pH-value: Should be between 6.5 and 9.5. To avoid corrosion, the pH-level should be kept between 8 and 8.5. Chlorination functions best at a pH-level below 8, requiring chlorination before alkalization. Small deviations from the limit values for pH does not cause any health hazard, but if the pH-value is above 11, it can cause cauterization damage especially to eyes and skin. See chapter 4.2.3. pH fluctuations may lead to loosening of biofilm, with high colony counts as a consequence.

The recommended higher limit value of 0.5 mg/l, is to prevent the water from smelling and tasting of chlorine. It is not hazardous to the health to use water with a higher chlorine level. The World Health Organization permits up to 5 mg/l, but in such cases it is recommended that the crew be informed that the water will smell and taste chlorine, see appendix 12.

Conductivity, see 6.4 : Abnormal conductivity levels should not be accepted on an offshore unit. Conductivity varies with type of water, depending on how the potable water is produced and where in the system the water is tested.

Total chlorine: Should be kept below 5 mg/l in water used for drinking. Water with higher total levels will smell and taste of chlorine. Adding as much as 5 mg/l should therefore be used only while disinfecting the pipe lines, see 9.2.6, as the Potable Water Regulations requirements for smell and taste are not fulfilled. During normal operations of the potable water system the total chlorine amount should not exceed 1.0 mg/l, unless it is necessary in order to reach adequate levels of residual chlorine.

In water production units, the measured conductivity level at the sample point of the production unit will indicate its functionality. The sample point from an evaporator shall not show conductivity higher than 6 mS/m (= 60 μS/cm). Modern evaporators often produce water with conductivity less than 1 mS/m. At the sample point from a reverse osmosis unit, a conductivity level up to 75 mS/m is acceptable, but modern osmosis units will produce water with much lower levels. Water with unusually high conductivity should be dumped.

4.3.2 Analyses when bunkering Water samples for quality testing should be taken from each one of the tanks the bunkering vessel delivers water from. Appendix 5 contains a suggested bunkering log. Before the water is accepted, the following parameters have to be measured and found acceptable:

When water passes through an alkaline filter, the conductivity level will increase. How much de pends on the type of alkalization unit being used, and it is important that conductivity levels have no abnormal variations. The cause of the abnormal fluctuations must be found. High levels of conductivity offshore imply high sodium chlorite content. See about sodium in 4.3.5.

Smell, taste, appearance and pH: See 4.3.1. Smell and taste are to be evaluated indoor, and appearance to be evaluated in good lighting.

Free chlorine : If chlorination is the only disinfection method in the potable water system, there should always be free chlorine in the water. If the potable water is treated with UV-radiation,

Conductivity: Water delivered offshore should not have a significantly higher level than water delivered from the supplying onshore water works. Normally Norwegian water works onshore have conductivity levels below 10 mS/m

21


(=100 μS/cm). Some onshore water works treat the water with alkaline filters to obtain conductivity between 10 and 15 mS/m. This water can be accepted offshore. The most important issue here is that there is no significant increase in conductivity during transport from the water works to the offshore unit. When entering into an agreement on water delivery to an offshore unit, the normal conductivity level for the onshore water works should be established, see appendix 6. Colour value: Should be below 20 (measured as mg Pt per litre). Higher colour value is normally caused by a high content of natural organic material (humic particles) in the water delivered by the water works onshore, see figure 4.4. High colour value reduces the effect of the disinfection, and may also cause formation of disinfection by-products.

Figure 4.4: Norwegian surface water often has a high content of natural organic material, requiring increased dose of chlorine when bunkering (Photo: Bjørn Løfsgaard) Turbidity: Shall be below 1 FNU. High turbidity makes the water unclear, normally due to a high content of small particles. The effects of disinfection is reduced, see 4.2.2, and the water appears less appetising.

Free chlorine: Must be verified 30 minutes after ended bunkering, see 4.3.1.

4.3.3 Monthly routine control

Clostridium perfringens: Shall not be present in 100 ml water. If the limit value is exceeded, the entire water system must be investigated to ensure that it is not contaminated by other diseasespreading substances with long survival abilities such as Cryptosporidium or norovirus. Clostridium perfringens can also cause food poisoning.

Monthly samples of water should be sent to an accredited laboratory. Procedures for this are described in appendices 7 and 8. A form for use in fault-finding, covering common deviations in potable water quality is shown in appendix 9. A sufficient number of samples from various points in the distribution network should be taken simultaneously to properly assess the water quality situation properly. In addition, operation analyses should be taken to enable control and adjustment of the potable water operations.

E. coli: Shall not be present in 100 ml water and if discovered, must be reported immediately to the authorities. E. coli has about the same life span in water as other common disease-producing intestinal bacteria, and is used as an indicator of such bacteria. Human faeces with high levels of E. coli, is the most dangerous microbiological contamination of potable water.

A suggested monthly minimum programme for potable water analyses is to take one sample from the potable water tank in use, and two samples from the distribution network. Sample points on the distribution network should differ according to a varied schedule. The sample points should include galley, hospital and the UV-unit outlet. One of the sample points in the distribution system should be a fixed reference point. The NIPH suggests a monthly water test programme with the following parameters:

If E. coli is found, immediate measures must be taken to avoid disease, see figure 4.5, and to prevent similar incidents in the future. Immediate measures will normally be a systematic check of the entire water system to ensure that it functions properly. Special attention should be given to disinfection. Are the chlorine level sufficient and is the UV-radiation unit functioning? When it has been established that all systems are functioning properly, new water samples should be analysed by an onshore laboratory. If malfunctions

Colour: See 4.3.2. Smell and taste: See 4.3.1.

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Has the water treatment malfunctioned or is the water quality outside normal values?

If E. Coli or intestinal enterococci are found, the authorities must be notified immediately

Yes

No

No The water quality is safe

New test to be taken immediately. Is the finding affirmed?

Use bottled or boiled water for drinking and cooking. Tanks and piping to be disinfected,see.appendi ces 12 and 13

New tests

No findings in two consecutive tests

Finding

Figur 4.5: How to act when E. coli or intestinal enterococci have been found in potable water samples (Illustration: Karin Melsom)

Coliform bacteria: Shall not be present in 100 ml of water. Finding coliform bacteria without finding E.coli normally indicates an older contamination without a great disease-producing potential. Even so, the same preventive measures as described for E.coli should be taken.

in the system are found, and can not be instantly remedied, immediate actions have to be taken to prevent disease outbreaks. Such actions usually include announcement via the PA-system, boiling of water, use of bottled water etc. The detection of E. coli must be followed by disinfection of contaminated tanks and pipe system.

Iron: Limit value is 0.2 mg/l (milligram/ litre). If the limit value is exceeded, it is an indication of corrosion in the potable water system. Generally this is not a health problem, but the iron value should be kept as low as possible because deposits of iron will possibly reduce the disinfection effect. High iron content will discolour the water itself as well as clothes and sanitary installations, and give the water an unpleasant taste. High iron content may indicate the possibility of other types of corrosion, i.e. of toxic heavy metals such as lead and cadmium.

Intestinal enterococci: Shall not be present in 100 ml of water. Finding intestinal enterococci indicate faecal contamination, and should be re ported immediately to the authorities. Intestinal enterococci have even better means of survival in salt water than E.coli, and are used as an indicator of disease causing intestinal bacteria. The same preventive measures as described for E.coli should be taken. o

Colony count 22 C/72 hour: Colony count in tanks and pipe system should be below 100/ml of water. Sample from the UV-outlet should be below 10/ml of water. In the colony count analysis, a wide range of micro-organisms, being naturally present in water, are found. Colony count count above 100 reveals a problem with microbial growth (biofilm) in the system, and must lead to investigations to disclose the cause of the problems and to find necessary corrective measures. Extensive biofilm can lead to bad smell and taste and reduce the effect of the disinfection. High colony counts are also a sign that the system may har bour microbes like Legionella, see 4.2.5.

Conductivity: See 4.3.1. Copper: Limit value is 1.0 mg/l, measured at the end of the copper pipe work. The copper values in hot water can be much higher than in cold water. Consequently the copper value is much lower when measured in the cold water fixture, after a short flushing. Copper values above 0.3 mg/l indicate that the alkalizing system is not working properly. The copper content in the cold water system should be maximum 0.3 mg/l. If water has been stagnant in the pipe system for

23

Sufficient, Sufficient, Safe and Good Potable Water Offshore

some time, it is not unusual to have levels above 3 mg/l, which can give acute gastrointestinal disorders. High copper content will give the water a bitter taste and cause discolouring of sanitary installations and sometimes give blond persons a greenish hair colour, see figure 4.6). Dissolved copper ions will also accelerate corrosion on other metals. High copper content may indicate the possibility of other types of corrosion, i.e. of toxic heavy metals such as lead and cadmium.

cyclic aromatic hydrocarbons and higher content than the above stated proves that the contamination has reached the potable water. It is most likely carcinogenic. Bromate: Shall be below 5 μg/l. By-product that may be formed when electro chlorinated sea water has passed an evaporator. Also found as pollutant after using hypochlorite that is not approved for potable water use, see 2.3.4. It may possibly be carcinogenic.

pH (acid value): See 4.3.1. Cadmium: Shall be below 5 μg/l. Higher content of Cadmium is normally a sign of corrosion on the pipe lines and fixtures. Cadmium is toxic and accumulates in the human body and affects many organs. It is suspected to be carcinogenic.

Supplementary analyses: Calcium: If an alkalizing filter, see 8.1, is used in the water treatment process, monthly calcium analyses samples should be sent to an onshore laboratory. The calcium value should be between 15 and 25 mg Ca/l. Such analyses indicate whether the operation of the system is optimal or not. High calcium content can lead to deposits in the UV-operation system.

Chemical oxygen demand (COD) (alternatively total organic carbon (TOC) may be measured): Shall be below 5.0 mg/l O (or 5.0 mg/l C for f or TOC). Shows how much organic material the water contains. It can cause microbiological growth and/or foul taste.

4.3.4 Extended yearly routine control An increased number of physical/chemical potable water parameters should be analysed in an accredited laboratory. Appendix 8 describes how the samples should be collected, but the laboratory should specify what type of bottles to use. The yearly programme should be carried out simultaneously with the monthly analyses and taken at the same locations on the distribution system (living quarter). The programme should include the following parameters:

Hydrocarbons, mineral oils: Shall be below 10 μg/l. May indicate contamination by protective coating (paints) or solutizers. This type of contamination is generally accompanied by an unpleasant smell and taste.

1.2-dichlorethane: Shall be below 3 μg/l (microgram/litre). Its presence indicates contamination by paint and/or solvents. Dichlorethane is mutagenic and possibly carcinogenic. Ammonium: Shall be below 0.5 mg/l. Higher levels can indicate contamination or defects in the production process. Its presence may reduce the chlorination effect. Benzene: Shall be below 1 μg/l. Benzene has been found offshore and is believed to be caused by contamination from protective coatings. Carcinogenic and also harmful in other respects.

Figure 4.6: Corrosive water in copper pipes can result in too high copper content in the potable water (Photo: Bjørn Løfsgaard)

Benzo(a)pyrene: Shall be below 0,010 μg/l. The environment may be contaminated by such s uch poly-

24

Sufficient, Sufficient, Safe and Good Potable Water Offshore

Lead: Shall be below 10 μg/l. High content of lead is normally caused by corrosion in pipe lines and fittings. Lead is toxic and accumulates in the body and affects many human organs.

4.3.5 Parameters without yearly analysis recommendation Basically, analyses of all parameters in the Potable Water Regulations should be carried out. Some parameters will, for various reasons, not be exceeded in an offshore potable water system. The Norwegian Board of Health has decided that offshore platforms, for the time being, do not need to analyse the following, see 4.3:

Polycyclic aromatic hydrocarbons (PAH): Shall be below 0.10 μg/l (includes the sum of benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene and indeno(1,2,3-cd)pyrene). indeno(1,2,3-cd)pyrene). PAH can be present in the potable water as a result of pollution originating some distance away or from activities on the platform. It is believed to be carcinogenic.

Acryl amide: Not applicable for Norwegian water. Aluminium: Not used in offshore water treatment and will consequently not be present in potable water produced offshore. The analysis requirements are fulfilled by analyses done by the onshore water works.

Tetrachlorethane and trichlorethen: Shall be below 10 μg/l. May indicate contamination by protective coating (paints) or solutizers. It can be carcinogenic. Trihalomethanes: Shall be below 50 μg/l (includes the sum of chloroform, bromoform, di bromochlormethane and bromodichlormethane). bromodichlormethane). These substances have been found on offshore units following electro chlorination in the sea water inlets. The substances are volatile and concentrations can increase in the evaporation process. Increased levels have also been found as a result of platform chlorination, when the water from the onshore water works already contains high levels of trihalomethanes. Chloroform and bromodichlormethane are most likely carcinogenic. More research has to be done before the other substances can be classified.

Antimony: Not applicable for Norwegian water. Arsenic: Not applicable for Norwegian water. Chloride: Shall be below 200 mg/l. Only to be measured if the values for conductivity are above normal. High content leads to corrosive water, unpleasant taste, and indicates sea water contamination. Conductivity measured after evaporation or reverse osmosis is mainly due to traces of sodium chloride (NaCl), and a conductivity of 1 mS/m implies a chloride content somewhat less than 3 mg/l Cl. Chrome: Not applicable for Norwegian water.

Supplementary analyses: Glycols: Shall be below 10 μg/l. Need only to be measured if there is a risk of such pollution through leakages from evaporators etc.

Cyanide: Not applicable for Norwegian water. Epichlor hydrine: Not applicable for Norwegian water.

UV-transmission: If UV is used for water treatment, yearly analyses of the UV-transmission should be done in addition to the analyses mentioned above. The analyses will document if the UV-intensity meter is working properly. Values for UV-intensity and UV-transmission should give parallel results (high levels for one, should show high levels for the other). Comparing results from previous years will reveal any discre pancy in the UV-intensity meter function, provided the water is of the same origin.

Fluoride: Only a problem in connection with ground water sources. No water works with fluoride problems deliver water to offshore units. The analysis requirements are fulfilled by analyses done by the onshore water works. Manganese: Only a problem with ground water sources, and no water works containing manganese deliver potable water to offshore units. The analysis requirements are fulfilled by analyses done by the onshore water works.

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Mercury: Not applicable for Norwegian water.

4.4 4.4 Drinki Drinki ng water in b ottles or other packaging

Nickel: Not applicable for Norwegian water.

Drinking water in bottles or other forms of packaging is increasingly popular. As a thirst quencher, in addition to normal intake of juice, milk, tea and coffee, water is recommended and unrivalled. Offshore potable water shall be of high quality and hygienically equal to bottled drinking water. From a health aspect it is not essential what kind of water people drink, more important is that they choose water instead of other, inferior beverages. Drinking water coolers placed where people gather, make it more tempting to drink water. Whether the water comes from a potable water system or is delivered in a water barrel has no significant health consequence. For those being cost- and environment conscious it is important to note that bottled water is extremely expensive compared to tap water. In addition packaging and transport of the bottled water makes it an environmentally bad choice.

Nitrate and Nitrite: Not used offshore. The analysis requirements are fulfilled by analyses done by the onshore water works. Pesticides: Not used offshore. The analysis requirements are fulfilled by analyses done by the onshore water works. Radon: Only a problem in connection with ground water sources. Even if ground water from onshore sources may perhaps contain radon, the amounts will be insignificant since the water is aired during transport. Selenium: Not applicable for Norwegian water. Sodium: Shall be below 200 mg/l, and should ideally be far below this level. Only to be measured if the values for conductivity are unnormal. High levels can be caused by failure in the production unit or the potable water being contaminated by sea water. An elevated sodium level is detected by high conductivity. The sodium content c ontent offshore is no problem to people with good health, but raised levels can be problematic for people on a low salt diet. High sodium content content increases blood pressure that may cause cardiovascular disease. Conductivity measured after evaporation or reverse osmosis is mainly due to traces of sodium chloride (NaCl), and a conductivity of 1 mS/m implies a sodium content somewhat less than 2 mg/l Na.

Some bottled water is labelled natural mineral water, and is covered by other rules and regulations. These products may have very high levels of sodium (figure 4.7). Bottled water used for daily consumption should have a low sodium level (labelled Na+ or Sodium). It does not make any difference to the health whether the bottled water contains carbonic acid or not.

4.5 4.5 Essenti Essenti al analys analys is equi pment Offshore units must have a minimum of water analysis equipment measuring: Chlorine: See 4.3.1. Free and total chlorine is measured in milligram per litre (mg/l). Normal chlorine values during operation offshore are 0.05 to 1 mg/l, but during disinfection of the system, values as high as 10 mg/l should be measurable. Certain measuring equipment is claimed to measure free chlorine values as low as 0.01 mg/l. Such low measured values may not be de pendable. The measuring requirement for free chlorine is thus set to a minimum of 0.05 mg/l, and the minimum requirement value must be above the limit the equipment is able to measure. Using a colour comparator makes it difficult to prove the exact value of free chlorine below 0.1 mg/l, therefore 0.1 should be used as the

Sulphate: Analysis is not necessary offshore as sea water contamination is revealed when measuring conductivity. Offshore water treatment does not carry risks for sulphate contamination. Total indicative dose: Not applicable for Norwegian water. Tritium: Not applicable for Norwegian water. Vinyl chloride: Not applicable for Norwegian water.

26


minimum value for free chlorine level. The chlorine measuring equipment on the unit should be able to measure chlorine levels of 0.05-10 mg/l, with precision requirements as follows: +/- 0.05 mg Cl2/l covering 0.1-1 mg Cl 2/l +/- 0.2 mg Cl2/l covering 1-10 mg Cl 2/l Colour: See 4.3.2. Measured in milligram per litre platinum (mg/l Pt) by using photometer or spectrophotometer, and the measuring equipment must measure colour values within 2-50 mg Pt/l. Conductivity: See 4.3.1. Is measured as milliSiemens per meter (mS/m) or microSiemens per centimetres (μS/cm). 1 mS/m equals 10 μS/cm. The measuring equipment must measure conductivity within 0-100 mS/m at 25 oC, with a precision requirement of +/- 5 %. PH-value: See 4.3.1. The measuring equipment must measure pH-values within 4-10, with a precision requirement of +/- 0.1 pH-unit.

Figure 4.7: Some natural mineral water has very high sodium content, as the conductivity gauge shows (Photo: Eyvind Andersen)

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5. General d esign requir ements Potable water systems shall be designed to give the crew sufficient quantities of high quality potable water at all times. Offshore potable water system differs from onshore systems in several ways, and requires special considerations.

1. Two sea water inlets supply the unit with water. This makes it possible to use sea water from different locations and different depths, thereby avoiding local contamination. 2. Two evaporators (or reverse osmosis units), each with 100 % production capacity, safeguard the water production even if one production unit is out of order. Produced water is dumped automatically if the conductivity (salinity) is too high, and in addition the water production units have a common conductivity meter and dump valve as extra safety

Failure in the offshore potable water system can have serious consequences since it is difficult to find other means of water supply. A water borne epidemic can infect so many persons within a short time, that it will become difficult to maintain operation on the unit. The potable water system is operated by regular offshore crew, with limited skills in how to operate such systems, compared to large onshore water works, where the operators hold special qualifications in water treatment. The HSE-regulations emphasise that potable water systems must be designed to minimize risks of failure as much as possible, by for example doubling crucial elements in the process, and choosing systems that are easy to operate, with minimal risks of technical malfunction

3. The alkaline filter makes the water less aggressive. CO2 added prior to the filter speeds up the process and stabilizes pH within the best values, see 4.2.3. 4. Two bunkering stations increase the possibility for bunkering in bad weather etc. Hoses can be flushed and samples taken before filling the tanks. Flushing of hose and pipe is to be done with the same water speed as when bunkering, and consequently the flush water pipe and valves diameter should match the capacity of the bunkering pipe. The piping needs a low point drain to facilitate complete draining of the pipes after bunkering.

When choosing a water supply system for an offshore unit, it is important to remember that potable water produced onboard normally is of very high quality, while bunkered water from an onshore source almost always contain natural organic material (humic particles), and thus is of inferior quality. Bunkered water will result in sludge and deposits in tanks and pipes, and may cause smell and taste problems and growth of micro-organisms, see chapter 4. It will also necessitate repeated and more time consuming cleaning, thereby increasing maintenance costs.

5. Flowmeter controlled chlorination equipment assures correct chlorination. 6. Two separate storage tanks assure available water even if one tank must be drained due to pollution, maintenance etc. The tanks have drain valves, but tank suction is placed higher to avoid tank sediment from entering the pipe system. Storage tanks and manholes are designed to make it easy for the maintenance crew to inspect and clean the tanks while the unit is in operation, see 5.2.1. Storage tanks, including air vents, are protected against penetration of sea water and other contamination, see 9.1.2. The pipes supplying water to the tank is located in a position that enhances water circulation in the tank. Automatic valves makes impossible to bunker water to a tank that at the same time is supplying the distribution network.

Design suggestions for offshore potable water systems can be found in chapter 5.1. A number of general requirements to design are given in chapter 5.2. Special advice regarding details is given in chapters 6 to 10 in the guideline.

5.1 Design example Figure 5.1 shows schematic how to design a potable water system. The numbers given on the drawing refer to the following text:

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4. Bunkering station

4. Bunkering station

Legend: Valve 5. Flow-meter controlled chlorine unit

Verifiable non-return valve Pump Manhole to tank Air ven t Filling/tap

3. Alkaline filter Automa tic cont rol of dumping valve

6. Potable water tank

6. Potable water tank

Pre filter 9. Return to tanks Verifiable reduced pressure zone valve

CO 2

Drain Three way valve 12. Circulation pump

11. To technical supply system. Note: This connection is atmospheric

2. Evaporator/ R.O. unit

11. To emergency showers or other pipes containing stagnant water 8. UV-unit

2. Evaporator/ R.O. unit

Y

7. Pumps

8. UV-unit

To living quarter

10. Water heater (70 oC) From living quarter (60oC)

1. Sea chests

Figure 5.1: Outline of an offshore potable water system (Illustration: Karin Melsom)

7. The system has two water pumps, each with 100% supply capacity.

times. The tank return inlet is located to enhance tank circulation. The water is automatically routed to the same tank that supplies the network.

8. Two or more UV-units which, even with one unit out of use due to maintenance or technical failure, still have sufficient capacity to disinfect the maximum water supply at the lowest relevant UV-transmission, see 8.3.2. The UVunits are equipped with solenoid valves that shut off the water flow if technical failure occurs. To avoid stops in the water supply, the units should be connected to emergency power supply. Particle filters are positioned in front of the UV-units to prevent microbes from passing the UV-unit in periods of turbid water.

10. Hot water circulates through a water heater holding a least 70o C to ensure that the temperature in the entire hot water system stays above 60o C, see 4.2.5. A verifiable reduced pressure zone valve prevents hot water from leaking into the cold water. Other connections to equipment where hot and cold water is mixed must be safeguarded as well. 11. Technical and other systems are not directly connected to the potable water system. Such connections are atmospheric or in other ways designed to prevent back suction of contaminated water, see 9.2.5. Stagnant water is to be avoided, and safety measures are to be located as close to the potable water branch-off as possible.

9. Tank return line (alternatively a hydrophore tank) provides stable water pressure in the pipelines. The return line is connected after the UV-units to prevent overheating of UVchambers by providing sufficient minimum flow in periods with low consumption of water. This solution may also improve the general water quality by letting the water pass through particle filters and UV-units several

12. The system has a dedicated pump with a large enough capacity to quickly circulate and chlo29


rinate water from one of the tanks, whilst water is being delivered to the distribution net from the other tank. The water is automatically pumped back to the tank of origin. Figure 5.2: During the construction process it is important that pipe systems are not contaminated. The picture shows how pipe ends are secured by being compressed (Photo: Bjørn Løfsgaard)

5.2 Directi ons f or desig n and constr uction of a potable water system The majority of necessary considerations when designing offshore potable water systems are obvious. Nevertheless, it is easy to make mistakes, either because not all aspects have been sufficiently considered, or because the potable water system is in conflict with other technical, economical or practical aspects. The NIPH suggests that persons in charge of the project use our check list in appendix 1, to evaluate if the project is in accordance with regulatory requirements.

•

•

Below we have listed the most important aspects to be considered in design of a potable water system. It is important to study closely all the different aspects throughout the planning and construction process (figure 5.2). By involving personnel with experience in operation of offshore potable water systems, many mistakes can be avoided.

•

•

5.2.1 Ergonomic design According to the Facilities Regulations §19.1 ”work areas and work equipment shall be designed and placed in such way that the employees are not subjected to adverse physical or mental strain as a result of manual handling, work position, repetitive movements or work intensity etc. that may cause injury or illness”.

•

Potable water tanks often have compartments and braces on the inside, making effecttive cleaning and maintenance difficult. Such obstructions should be avoided if possible, or be designed to make access easy, and to make flush water drain away properly (figure 5.3). Potable water tanks are often constructed with very high or low walls, this obstructing cleaning and maintenance. With high walls, ladders and platforms can be built inside the tank, but such equipment must also be constructed to facilitate cleaning and maintenance. The design of alkalizing filters often makes it awkward to fill or empty the filter as this frequently involves climbing and heavy lifting. Access to the filter for inside maintenance may also be difficult. Manholes for potable water tanks and hydro phore tanks are difficult to reach, especially when heavy equipment is needed for repairs inside the tanks. Sections of the potable water system requiring regular attendance are often placed in areas with disturbing noise levels.

The requirement to ergonomics applies to the entire potable water system, operations as well as maintenance. Insufficient ergonomics measures can result in necessary work operations not being undertaken in a proper manner. The NIPH often has experienced inferior ergonomic design in the following situations: •

•

The flush valve on the bunkering station is often placed in such a position that the crew on the unit or the supply vessel crew is subject to heavy gushes of water. Valves, that are opened or closed often, are placed in awkward positions.

Figure 5.3: This tank has a drain well, and the stiffeners are placed vertically, with drain cavities against tank floor. Consequently the tank is easy to drain (Photo: Eyvind Andersen)

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5.2.2 Safeguarding against mistakes

5.2.4 Hygienic barriers – preventing contamination

According to the Facilities Regulations § 19.2 ”workplaces and equipment shall also be designed and placed in such manner that the danger of mistakes significant to safety, is reduced”. Supply of sufficient, safe and good potable water is a prerequisite for the unit to be operated safely, and the unit must be designed to minimize probability of mistakes that could jeopardise the water supply.

A fundamental principle in Norwegian water supply, is the requirement for at least two inde pendent hygienic barriers against the various contaminants that could occur in a potable water system, see the Potable Water Regulations § 14. The barriers ensure, even if one barrier fails, that the water quality will still be satisfactory, since the second barrier should not fail for the same reasons as the first one. The following are examples of hygienic barriers in a potable water system:

The potable water system should be based on the use of simple and robust technical solutions, see the Facilities Regulations § 4. Technical solutions with many different and complicated details that may fail should be avoided and simple solutions chosen, thereby eliminating risks for failure, and also minimizing the risk for human errors. Listed below are solutions that should be avoided:

•

•

• •

•

•

•

•

Technical solutions where one mistake can cause important systems to malfunction, such as bypassing the disinfection units. Technical solutions requiring intensive supervision to function properly. Technical solutions not functioning under unstable conditions, like changing water quality. Technical solutions where failure is difficult to uncover, or where it is difficult to limit the damages and do repairs. Technical solutions where it is stated: ”We know this might easily fail, but we have a procedure that will prevent failure”.

•

Something preventing contamination of sea water used in potable water supply, see 6.1.1. Something diluting sea water contamination to a harmless concentration before the water reaches the sea water inlets, see 6.1.2. A treatment process rendering harmless or removing microbes, braking down, removing or thinning chemical and physical substances. See 6.2 and 6.3 regarding evaporation and reverse osmosis, and chapter 8, about water treatment in general. Precautions taken in the distribution system to prevent already treated water from again being contaminated, see chapter 9.

Numerous types of pollution can influence the potable water quality from the sea water inlets through the treatment units to the distribution system. To secure two hygienic barriers against all types of pollution throughout the entire process is a demanding task. Important actions could be:

5.2.3 Storage capacity requirements Offshore units must always have enough water aboard. The minimum daily supply is 200 litres potable water per person for drinking, cooking, personal hygiene, cleaning etc. Storage capacity should be large enough to supply these needs even if water delivery is interrupted. The storage tanks should be of equal size, and requirements for total storage capacity depend on number of tanks and water production capacity, see section 9.1.1.

•

•

If the water is stored too long, bad taste and smell may develop. The storage tanks should be operated to prevents this, and the water should not be stored more than 20 days. Under normal operation the tanks all tanks can not be emptied at the same time, and the minimum storage reserve is two days of maximum water consumption.

•

31

Sufficient safety measures for sea water inlets require restrictions in the discharge of polluted water from the offshore unit. Polluted waste water should be diluted and the sea water inlet located in the most suitable place considering water depth, polluted discharge water and common current directions, see 6.1. These safety measures equal at least one barrier against most types of pollution. Water production through evaporation or reverse osmosis is considered as a barrier against most types of pollution, see chapter 6. The hose connections and routines for bunkering water from the onshore supply source represent a weak element in the delivery chain, but transport safety routines, and flushing and taking water samples at the bunkering station,


•

•

•

can provide two barriers against physical and chemical substances, see chapter 7. Transport and bunkering routines are important, but are not considered a reliable hygienic microbial barrier. Chlorinating the water when bunkering is therefore necessary in order to secure one barrier against microbes, see 7.2. The other microbe barrier is normally UV-radiation of the water passing from storage tanks to the distribution system, see 8.3. It is vital to prevent the potable water from contamination on its way to the consumers. Atmospheric connections or equivalent solutions, see 9.2.5, prevent contamination from a variety of technical devices using potable water. Contamination via leakage or pollution through chemical dosing tanks or air vents must be avoided by placing tanks in areas separated from other contamination sources.

5.2.6 Location of sample points In case problems in the potable water system occur, it is important to be able to locate the exact position of the problem and how far it extends. A sufficient number of strategically placed sample points along the entire system are necessary. These sample points should be placed on bunkering stations, storage tanks, and subsequent to each main component in the system, such as production unit, disinfection unit, alkalizing filter and other treatment units. Placing, marking and protection of equipment are described in 5.2.5, but he following should be observed: Piping from main pipeline to sample valve should be as short as possible to avoid stagnant water. Piping after sample valve should be self draining, as short as possible and shaped to enable easy disinfection by means of chlorine, alcohol or heat. End cap on pipe is recommended.

The potable water system should be designed to minimize the risk of contamination. Examples on solutions to be avoided are given in chapter 5.2.2.

5.2.7 Paints and protective coatings Paints and coatings being used in storage tanks have often contaminated the potable water by im proper use and shortened hardening processes, see 9.1.4. Paints and other protective coatings shall be certified, see chapter 2.3.4, and the owner must be able to document that such products have been applied according to certification requirements and the manufacturer’s instructions, see 9.1.4.

5.2.5 Placing, marking and protecting the equipment Detailed descriptions are given in chapters 6-10. According to the HSE-regulations, the following general design requirements apply: •

•

•

•

•

•

•

Important operation equipment, valves etc. shall be marked and easily accessible. Design of technical equipment and work areas shall make maintenance operations easy. The equipment shall be protected against pollution from other process equipment. Potable water pipes and storage tanks shall be physically secured and clearly marked and colour coded to make following easy in case of an emergency, and to prevent link up with other fluid systems by misunderstandings etc. Tanks for additives are secured by using screw cap or equivalent and marked to avoid pollution by accidents etc. (figure 5.4). Sections of the potable water system placed outdoors should be of non-corrosive material. The entire potable water system must be of a non-corrosive material adjusted to the corrosivity of the potable water, see 9.2.3.

5.3 Alterations of t he potable water system When a potable water system is altered, reconstructed or taken out of operation, it is necessary to assess whether the entire system still fulfils the requirements to offshore potable water systems. Significant changes must be reported to the authorities, see Information Duty Regulations § 5.

Figure 5.4: A marked and protected chlorine tank with easy access (Photo: Eyvind Andersen)

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6. Potable water pr oduc tion

Wastes containing oil: Production water discharge, deck flushing water, oil wastes from own or adjacent units, are potential sources for oil pollution. Such pollution can give an unpleasant smell and taste to the water even in very small quantities, and may also damage production units.

Potable water on an offshore unit is produced either by reverse osmosis or evaporation. Such water must be treated to become non-corrosive to the pipes and fittings, see chapter 8.1. It is important to make sure that the sea water used in the production is not polluted. If polluted sea water is suspected, the water production must stop.

6.1 Sea water i nlets

Chemical discharge: This might come from the same sources as the oil wastes and create the same type of problems. Volatile chemicals can pass an evaporator and the concentration might increase.

A sea water system normally has two sea water inlets. The water is pumped through sea water pipes for the various types of use, for instance fire fighting water, production unit for potable water and a variety of technical needs. The sea water must be protected against pollution.

Growth of micro-organisms: Periodically some organisms have an intense growth in sea water. Some will emit volatile components into the sea water, causing problems with smell and taste in the produced water. This occurs mostly in the summer and autumn.

6.1.1 Possible pollution threats

Electro chlorination of sea chests: This method of marine growth prevention increases the risk of exceeding the limits for bromate, trihalomethanes etc. when water is produced through evaporation. To minimise such problems, the company must make sure that the electro chlorination is being done without overdosing of chlorine in periods with low seawater consumption. The company must also establish a sufficient analysis programme to document that the electro chlorination is conducted without posing any health risks.

Sea water used in the potable water production might be polluted. The reasons could be discharge from own or adjacent offshore units, or discharge from ships. Water production should not take place when the water is polluted or when the unit is near harbours etc. The following pollutants are the most common: Sanitary waste: Sewage and waste water from living quarters contain nutrients and various microbes. If such elements get into the potable water system they can lead to growth of biofilm in storage tanks and pipes, problems with smell and taste, and in worst case, disease.

6.1.2 Placing sea water inlets Placing sea water inlets require documentation that the discharges from the unit will not cause unacceptable levels of pollution. In order to assess the pollution threat, it is necessary to analyse the dispersal area using a recognized model, see Management Regulations § 13. If several of the factors listed below are uncertain, the safety limits should be set high. The following measures should be taken to prevent or reduce pollution: Sea water inlets to be located as far away from the discharge points as technically feasible. When waves hit the platform legs the result is a strong shift in the water masses (figure 6.1). Discharge beneath the platform ends in turbulent water masses that can cause spreading and thinning of pollution both horizontally and vertically. Sea water inlet and discharge points should be located on separate platform legs/pontoons, preferably the

Figure 6.1: Normally there is turbulence in the water around the platform legs. Sea water inlets should be placed where the danger of pollution is at a minimum (Photo: Eyvind Andersen)

33


Several sea water inlets operating separately should be installed. The unit should have at least two sea water inlets spaced well apart. When local currents change so that polluted discharge water is directed towards the sea water inlets in use, the other sea water inlet should be used.

sea water inlet on the outside of the leg and the discharge on the inside. By placing sea water inlets deep down, the influence from the surface is slight, temperatures are low and fewer microorganisms exist. Placing sea water inlets favourable to currents The sea water inlets should be placed upstream of the discharge point, considering the most common current direction (figure 6.2).

Other sea water connections must be placed in a way that does not lead to contamination of the sea water pipe system by back-flow or backsuction. The sea water inlet can be secured by being the first connection on the sea water system and securing other branch-offs with non-return valves. The best solution is to have separate closable sea water inlets for production of potable water, as common inlets for sea water supply tend to be used also in ports etc, and thus pose a risk of contaminating the water supply for potable water production. Such separation is particularly important for units that have diving systems, as these are more vulnerable to the effects of contamination.

Figure 6.2: Sea water inlets must not be placed downstream from the discharge points, taking into account the prevailing current direction. Inlets should not be placed on the same side of the unit as the discharge. The inlets, as illustrated above, should be moved to the outside of the pontoons. (Illustration from B3/NIVA’s engineering office)

6.2 Evaporation Evaporation is the most common method used in potable water production on the Norwegian Continental Shelf. The evaporation process means that sea water is heated until it evaporates and is thereafter cooled off, resulting in fresh water. There are different types of evaporation units, but only vacuum distillation will be described here, see figure 6.3, this being about the only type of evaporation unit in use on the Norwegian Continental Shelf.

Discharges with equal physical characteristics should be gathered together. A discharge with a different density than the surroundings it is discharged to, can move significantly in vertical direction before being diluted. A high density discharge is therefore expected to sink, and should consequently be placed below the sea water inlets. On the other hand, a low density discharge should be placed higher up. Vertical separation of sea water inlets and discharge is easier to achieve on offshore units placed on the sea floor. Design and size of discharge pipes are key elements in the way discharge water is spread and diluted. A pipe ending in many small holes, like a diffuser, will greatly increase dilution com pared to an open pipe with the same diameter. The concentration of pollutants will be lower with an efficient dilution.

Figure 6.3: Design principals for a vacuum distillation unit (Illustration from B3/NIVA’s engineering office)

34


Figure 6.5: The drawing shows process principles for osmosis and reverse osmosis (Illustration from B3/NIVA’s engineering office)

6.3 Reverse osmosis

Reverse osmosis is a process where sea water is forced under high pressure against a membrane with microscopic openings. The water molecules are very small and will pass the membrane, but most of the salt and other contaminants will be held back. Potable water produced by reverse osmosis will have a higher salt concentration than water produced by evaporation. Production costs for an evaporation process are normally higher than for reverse osmosis, except for units that can utilize cooling water for heating. The higher the salt concentration is, the more corrosive water, and it is therefore important to use high quality pipe material in the system, see 8.1.

Figure 6.4: Shows the inside of an evaporator. The net prevents sea water drops from passing on to the distillate (Photo: Bjørn Løfsgaard)

When pressure is reduced, the evaporation temperature is lowered to between 30 and 60 o C. Sea water is pre-heated in a heat exchanger with hot distillate. The feed water is then led into the condenser where the water accumulates condensation energy from the steam. Heated feed water is led into an evaporator and heated with an external source, starting the vaporization process (figure 6.4). Hot water, steam or electricity is used as a heating source. For units with plenty of hot cooling water, for example from diesel engines, this could be used in heating the water, and in such cases evaporation will be a less expensive production process than reverse osmosis. The low evaporation temperature reduces problems with boiler scale and reduces the need for chemicals.

The principles for osmosis and reverse osmosis are shown in figure 6.5. When two solutions with different salt concentrations are separated by a semi permeable membrane, the water with the lower salt concentration will flow towards the water with the stronger salt concentration. This process is called osmosis. The water level remains higher on the side with the high concentration of salt. The difference between water levels is called an osmotic pressure. In reverse osmosis the pres-sure applied on the salt concentration is higher than the osmotic pressure. Fresh water will consequently flow from the high salt concentration into the lower salt concentration. Because the sea water salt content increases during the pro-cess, the concentrate must be drained into the waste water system and new sea water supplied.

If the sea water is polluted, substances more volatile than water may pass the evaporator while other substances and microbes only pass in case of operation failure. As only some of the feed water evaporates, while it is assumed that all volatile substances will evaporate, this can result in concentration of such components in the produced water. When the sea water is electro chlorinated prior to evaporation, see 6.1.1, problems with chlorine and bromine compounds like bromate and trihalomethanes may occur see 4.3.4. Such problems may be minimised through better operation of the electro chlorination, and through reducing the effect of the evaporator, thus producing cleaner water. Volatile substances can be removed, see 8.4.

Reverse osmosis is safer than evaporation in eliminating contamination, but if the membranes are damaged, micro-organisms and other substances can slip through. Membranes vary in design, see figure 6.6. To avoid damage to the membranes by 35


pollutants in the sea water, the water requires treatment. At the sea water inlets chlorine is often added to reduce algae/bacterial growth in the system. Chlorine residues can damage the membranees, but this can be avoided with an active carbon filter. The feed water might contain particles too small to be stopped in the sea water inlet filter, but large enough to clog the fibre membranes. Particles down to 5 micrometers must be removed. This can be done by using different filter types. To reduce the manual maintenance work, the flushing and cleaning process should be automatic.

(Photo: Bjørn Løfsgaard) The conductivity meter shows the conductivity in mS/m, μS/cm or as ppm sea salt (1 mS/m = 10 μS/cm = 4,6 mg/l NaCl). The conductivity meter should be a type where the setting can be adjusted and controlled. A tap should be placed on the outlet to make it possible to cross check the conductivity meter with another conductivity meter.

6.5 Use of chemic als All substances used in the potable water process shall be certified, see 2.3.4. Filling pipes used for adding chemicals shall have close-fitting caps to avoid contamination.

6.4 Conducti vity c ontrol To ensure that water produced by evaporation or reverse osmosis is safe enough, conductivity is measured at the production unit outlet. Sea water has a high conductivity level, and a possible malfunction in the production process can be detected by a rise in the conductivity (figure 6.7).

Evaporator operation requires the use of chemicals. The chemical can either be added continuously, for example scale inhibitor added to the feed water to prevent boiler scale on hot surfaces, or intermittently, such as in the cleaning process. Chemicals are also used indirectly as the heating medium for the evaporator often contains hot water or steam, to which the chemicals are added to prevent boiler scale, corrosion and possible freezing. Chemicals are seldom continuously added in an osmosis process. Occasionally chemicals are used in cleaning the membranes, and for preservation, as membranes can easily be damaged when not in use.

The conductivity meter, also called salinometer, is placed at the production unit outlet. Conductivity determines the quantity of salt in the water. The limits are set in advance at maximum 6 mS/m for the evaporator process and 75 mS/m for reverse osmosis. If the limits are exceeded, the water distribution to the tanks should be stopped and the alarm activated, as this indicate that the system is not operating as it should be. Conductivity is described under chapter 4.3.1. There have been several incidents where malfunctions in conductivity meters or dump valves have resulted in salt water contamination of the potable water. This is a hygienic problem, and also results in much work to re-establish good potable water quality. It is recommended that water production units are equipped with two stages of conductivity metering and dumping, see figure 5.1.

Figure 6.7: A conductivity meter automatically measures salt content in produced water and dumps it if the 6 mS/m limit is exceeded (Photo: Eyvind Andersen)

Figure 6.6: Reverse osmosis unit with the membrane placed in the roll on top of the unit

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7 Bunkering potable water When bunkering water from supply vessels, it is difficult to have full control of the water quality. The water may be contaminated when delivered to the supply vessel, or contaminated during trans port to the offshore unit. Contamination can happen both onboard the supply vessel and in the bunkering process through for example dirty hoses. Tests at the bunkering station have occasionally revealed pollution by sea water, diesel etc.

should be designed to ensure that the pipes are drained completely after bunkering is completed. Both bunkering stations and hoses have to be marked to avoid confusion with hoses for other liquids, and the bunkering stations for potable water should be separate from bunkering stations for other types of fresh water. Bunkering hoses (1) are either coiled up on a drum, or hanging down the sides of the unit. The couplings are susceptible to pollution from sea water, various processes onboard and pollution from birds. Dead birds have been found in potable water pipes. It is therefore important to cover the hose ends. It is also important that the hoses are equipped with a floating device to prevent them from contact with the supply vessel propellers. Hose connections for potable water should be of a distinct design to prevent contamination by connecting the wrong hoses.

All water delivered by supply vessels is of uncertain quality regardless of precautions taken by the supplier and recipient. The biggest uncertainty is connected to microbiological contamination, as it is not possible to take such samples when bunkering. Consequently it is important that all potable water is disinfected during bunkering. Frequently the colony count increases in the entire potable water system after bunkering. It is significant to check the disinfection units and control routines, as each disinfection unit should separately be able to deactivate the majority of microbes in the water. Even though the unit is responsible for poor water quality after bunkering, the danger of bunkering inferior quality water is reduced if the owner requires that supply bases and supply vessels have good routines in drawing and transporting the potable water, in addition to satisfactory cleaning and maintenance of the storage tanks, see appendix 6.

Bunkering hoses are normally made of rubber, an organic material that may serve as ”food” for microbes. Dark coloured hoses warm up fast in the sunlight, and there will always be moisture inside, resulting in excellent growing conditions for microbes. The hoses should be flushed thoroughly before each bunkering, and after bunkering they should be drained before they are hanged and stored (figure 7.1). Hoses are difficult to clean and should therefore regularly be exchanged.

7.1 Design of b unkeri ng sy stem, including water circulation Figure 7.2 shows a bunkering system with the possibility for circulating water from one storage tank, through to the chlorination unit, back to the same storage tank, without feeding the water into the distribution system. The numbers in the text below refer to details in the figure. Interlocks or other measures ensure that water is bunkered and circulated into other tanks than the one that is supplying accommodation, see 5.1. Figure 7.1: Bunkering hose for potable water. The hose has light colour in order to reduce warming. Both hoses in the picture have floating devices to prevent entangling in the supply vessel propellers (Photo: Eyvind Andersen)

An offshore unit should have two bunkering stations, preferably placed on each side of the unit, to increase the possibility to bunker during bad weather conditions. The bunkering pipe system 37

Sufficient, Safe and Good Potable Water Offshore 3. Shut-off valve 4. Test tap Legend: Valve 6. Chlorination unit with flow-meter

Verifiable non-return valve

1. Bunkering hose 2. Flush pipe

Pump Manhole

10. Drain

Air vent

Supply ship

filling/ flushing

7. Potable water tank. The tank inlet enhances tank circulation

Drain Three way valve

8. Test tap

5. Tank drain

9. Circulation pump

10. Drain

To UV-unit

Figure 7.2: Drawing of a bunkering system with recirculation pipe (Illustration: Karin Melsom)

At the connection point for the bunkering hose a flush water pipe (2) should be installed as well as a shut-off valve down stream on the feed pipe (3). Sudden increase in water flow results in contaminants being dislodged from the walls of pipes and hoses. To prevent increase in water flow after flushing, the flush water pipe dimension must be at least as large as the feeding pipe. Bunkering stations should be designed to prevent operating personnel on the unit or the supply vessel crew from being sprayed with water in the flushing process. The test tap (4) is placed in front of the shutoff valve on the flush water pipe. It may be located on the feed pipe and should be easily accessible for sampling. Discharge of old potable water from storage tanks (5) is advisable before bunkering takes place. This will wash out the sediment and make chlorination more effective, see 7.2, and will also reduce the amount of chlorination by products, as all water is chlorinated only once.

This will result in more efficient chlorination of the water as the chlorine also reaches any “old” water in the storage tank, and will also make tank recirculation easier to achieve. Test taps (8) makes it possible to sample the chlorinated water in the tanks, without simultaneously feeding this water to the consumers. Test taps should be easily accessible. Operation, maintenance, design and other requirements for storage tanks are described in detail in chapter 9. A large capacity circulation pump (9) provides the possibility for a fast circulation of water from one storage tank, via the chlorination unit and back to the same tank, without having to distribute it. Simultaneously, water will have to be distributed to the network from another tank. This makes it easy to dose extra chlorine to bunkered water that have received too little chlorine during bunkering. Without this option, bunkered water with no residual chlorine will have to be dumped and tanks refilled, and this increases the risk of running out of water. Circulation is enhanced by separating the tank inlet and outlet. It is preferable to design this distribution system to let the water pass the alkalizing filter as well, see 8.1. Low point drains on the bunkering and circulation pipes (10) make it possible to avoid stagnant water after bunkering.

A chlorine dosing pump (6) is connected to the bunkering pipe system, see 8.2.4. The best mixing ratios are achieved if the chlorine pump is controlled by a flow-meter. Bunkering pipes should be designed in a way that enhances water circulation in the tank (7), for example by separating the inlet and outlet, and by pointing the inlet in a direction that enhance circulation of the total tank volume. 38


1.

7.2 Disinfection requirements Disinfection of potable water is done by adding chlorine. Chlorination is described in detail in chapter 8.2. To achieve sufficient disinfection, the chlorine must be well mixed with the water. It should be evenly distributed into the water flow during the entire bunkering process. Often the shape of offshore potable water tanks result in inadequately disinfected water, because of insufficient mixing when chlorine is poured directly into storage tanks before bunkering (figure 7.3). To achieve the best possible chlorine-water mixture in the entire tank, it is best to start the filling process with tanks being as empty as possible.

2.

Figure 7.3: Pouring chlorine directly into storage tanks may result in lack of chlorination in parts of the tank and overdosing in other parts (Illustration: Bjørn Løfsgaard).

7.2.1 Flowmeter regulated dosing A flow meter on the bunkering pipe adjusts the chlorine pump speed. The pump doses a calculated amount of chlorine per cubic meter water. To chlorinate bunkered water adequately, the concentration of the solution must be adjusted. If normal procedure is to bunker to an empty tank, the same chlorine concentration can be used each time. When bunkering to a tank with residual water (to be avoided if possible), the chlorine concentration should either be increased to chlorinate the residual water as well, or the volume of chlorine that the flowmeter is set to give, will have to be adjusted.

7.3 Bunkering procedures Appendix 10 gives advice for bunkering. These issues are further discussed below.

7.3.1 Prior to bunkering Before bunkering starts, an adequate amount of chlorine solution with the correct concentration should be prepared, see appendix 11, with details on how to calculate dosing for various chlorination methods. The dosing should be adjusted according to experience from previous bunkering, achieving a sufficient chlorine residue relevant to the water quality being bunkered, see 7.4. The chlorine amount is adjusted by changing chlorine concentration or through modification of the volume of chlorine solution being added. If the pump is not Flowmeter regulated, the dosing speed must be calculated, see appendix 11.

7.2.2 Dosing with a manually regulated pump This method offers greater flexibility in choosing the concentration of chlorine. If the chlorine solution is concentrated, the pump speed is slow, and if the chlorine solution is diluted the speed is increased. It is recommended that a diluted chlorine solution is used, since this will result in a better mixing of the chlorine in the bunkering water stream, due to higher speed and volume of the injected chlorine water. When using a manually regulated pump it is necessary to know how long the bunkering will take, and adjust the chlorinateon pump speed to deliver the necessary chlorine dose for the entire time span. If bunkering to a tank with residual water (to be avoided if possible), enough chlorine should be added to chlorinate the residual water as well. This can be achieved by increasing the chlorine pump speed or by increasing the concentration of chlorine solution.

It is important to make sure that all valves are in correct positions, see 3-6 in appendix 10. Bunkering should always be done to tanks as empty as possible. This is particularly important when bunkered water has a high content of organic material. If it is possible to dump the residual water in the tanks prior to bunkering, it will make the chlorination procedure easier and reduce troubles with colony counts, chlorination by-products and other pollution of tanks and pipe system, see 4.2.2.

7.3.2 Bunkering Bunkering starts by flushing the hose and piping a few minutes under maximum pressure (figure 39


7.4). After flushing, a sample is taken to determine colour, smell, taste, appearance, conductivity and pH of the water, see requirements in chapter 4.3.2. Water that does not fulfil the requirements should be rejected (figure 7.5). If a supply vessel delivers water from more than one tank, samples should be taken from each one of the tanks. If the water is acceptable, the bunkering can start.

not ideal, since it might be difficult to mix the chlorine satisfactorily in the water. It is recommended that the chlorine dosage is set higher than the minimum requirements to avoid such unfortunate situations. It is reasonable to aim for a free chlorine level of 0.3 mg/l after 30 minutes. If the concentration of free chlorine is too high, the water can be diluted with water from other storage tanks. The water can also be stored before being consumed. The chlorine concentration will then decrease. There is no health hazard involved by using water with a chlorine concentration up to 5.0 mg/l, but the water will smell and taste chlorine, and this should be avoided if possible. In case the water has to be used, the crew should be informed of the situation beforehand, see appendix 12 about disinfection of pipe systems.

7.4 Log gin g It is important to keep a log of the various details in the bunkering procedure. This permits adjustments ahead of the next bunkering. Experience shows that many water quality problems are connected to bunkering, either due to poor water quality from the water source, or because the bunkering process is inadequate. The bunkering log is an important tool in solving such problems. Appendix 5 shows an example of such a log.

Figure 7.4: When flush valve and the bunkering hose have corresponding diameters the system can be flushed with maximum pressure. (Photo: Eyvind Andersen)

7.3.3 After bunkering The storage tanks are to be isolated for 30 minutes after bunkering, then a sample should be analysed for the free chlorine. The results should be between 0.1 and 0.5 mg/l, see 4.3.1. The free chlorine evaporates after some time. It is important that the sampling is done within a reasonably short time, otherwise it might be impossible to document that the water is disinfected. If no free chlorine is found after 30 minutes, the water must either be dumped or more chlorine added by circulating the tank content via the chlorination system, if the unit design permits this, see chapter 7.1. The water should circulate until the chlorine is mixed properly, and another sample taken 30 minutes later. This is repeated until free residual chlorine can be measured. This practice is

Figure 7.5: Determination of smell, taste and appearance must take place indoors and under strong light to have any value (Photo: Eyvind Andersen)

40


8. Water t reatment Both bunkered water and water produced from sea water have to be treated to make sure that the quality requirements in the Regulations are met. A range of methods can be used to accomplish this. In this chapter the most frequently used methods are described. All additives to the potable water, such as chlorine, filter material, cleaning agents etc. have to be certified, see 2.3.4.

Units with CO2-dosing ahead of the alkaline filter will increase the calcium/hydrogen carbonate content (HCO3 ), and stabilize the pH within the most favourable limits. Units without CO 2-dosing will have more fluctuation in the pH level both in production and in the pipe system. Design Figure 8.1 shows a filter with the inlet at the top and the outlet at the bottom. This type of filter must always be designed for return flushing. The flush water is led from the distribution net in to the bottom filter, lifting the masses, and is then discharged via the flush drain. High pressure is necessary when flushing. Using the same pump that feeds the water through the filter during normal operation does not always result in adequate pressure. The flush water has to be of potable water quality. The filter must be designed with a filling hatch and a drain hatch, and it must be possible to drain and empty the filter to clean it. Protective coating inside the filter has to be certified for use in potable water systems.

Potable water produced from sea water must be treated to make it less corrosive, see chapter 8.1. All offshore potable water has to be disinfected. The disinfection process inactivates contagious microbes. Disinfection offshore is done through chlorination or UV-radiation, see 8.2 and 8.3. Bunkered potable water is disinfected by adding chlorine during bunkering. In addition, both bunkered and produced water shall be disinfected as it is being distributed to the consumers. UV-radiation is generally used in this process, but some offshore units disinfect the water by ensuring that there is free chlorine in the potable water. The NIPH no longer recommend disinfection only by use of chlorine, as UV-treatment has been proved more effective against some microbes, se 8.3.

Dolomite filter (half burnt dolomite) Filters with half burnt dolomite are the most compact and therefore often used offshore. The

8.1 Corrosi on control Flush/Vent valve

Corrosion in a potable water system means that the water attacks metal in the piping system, treatment units and fittings, much in the same way as a car becomes corroded by climatic factors. Corrosion causes, chemistry and health consequences are described in chapter 4.2.3. Corrosion reducing water treatments are described below.

Filling hatch

Inlet valve

From water production unit

By-pass valve From potable water pump

The most common method in offshore corrosion control, is to let the water pass through a dolomite mass or limestone filter. Sodium silicate has also been used with good results, and does not require any filter.

Drain hatch

Outlet valve Shut off valve

8.1.1 Alkaline filter

Drain valve

Alkaline filters are recognized under different names, for example palatability filter, limestone filter, marble filter and re-hardening filter. The filters may be designed in a variety of ways and using a range of filter materials.

To potable water tanks

Test tap

Drain

Figure 8.1: The filter has to be designed with easy accessibility for cleaning, changing of filter mass and maintenance. (Illustration: Karin Melsom)

41


water passes through the half burnt dolomite, Ca(CO3)MgO, and part of the mass dissolves in the water. By dosing CO 2-gas to the water prior to the filter, a higher hardness and alkalization is achieved, simultaneously stabilizing the pH level around 8. Without the CO 2-gas, this filter mass can result in extremely high pH levels (pH 11-12), and is therefore not advisable. The effects of the filter mass decrease after a while. To begin with, a rapid release of MgO results in high pH values, while aged masses mainly contain CaCO 3, which is less soluble in water and thereby less effective. New filter mass must be added continuously and the entire filter mass changed regularly.

give just about the same corrosion protection as alkalization. The effect depends on the water quality and material in the pipe system. Using sodium silicate is especially useful in a pipe system of acid-proof stainless steel, where the feeding pipes to drain taps are made of copper. If sodium silicate is used in systems with galvanized iron, the corrosion compounds are washed away into the water before the water quality stabilizes. Sodium silicate functions best in acid and soft water. Necessary sodium silicate dosage escalates with increased concentration of salts and increasing hardness and temperature in the water being treated. The precise mechanism in this process is not well known. Silicate ions can prevent metal ion deposits like trivalent iron, thereby reducing rust bulbs in iron and steel pipes. Sodium silicate can also grow a film of precipitated silicic acid and metal silicates on the pipe surfaces, and eventually prevent corrosion.

Limestone filter/marble filter Crushed lime stone (CaCO3, marble) is used in the same way as dolomite, but being less soluble and due to its chemical composition, the pH level will not reach as high levels as the dolomite. New filter mass will bring the pH value up to around 8.5 without adding CO 2, and with CO2 pH it stabilizes around 8. To obtain a sufficient solution of limestone, it is important to have a large contact surface. A particle size of 1-3 mm and a filter depth of at least 1 m are common. It is also important that the strain on the filter is not too intense, resulting in an insufficient contact period. Marble filters are easy to operate, and have the advantage, compared to other methods, of keeping the pH below the maximum limit. Marble has to be replenished regularly to keep up an even mass grading.

Sodium silicate is supplied dissolved in water, and must be certified, see 2.3.4. Dosing is normally done with a flowmeter regulated pump. This system is easier to use than alkalizing filters, and the risk of microbiological growth is avoided. The dosing point should be placed after UV-units.

8.2 Disinf ection by ch lorin ation Chlorine is still the most commonly used product in disinfection of potable water world wide, and chlorination of potable water offshore does not pose any health hazard, see chapter 4.1.2. Offshore, calcium hypochlorite (Ca(OCl) 2) and sodium hypochlorite (NaOCl) are used. The two form the same active chlorine combinations in water, hypochlorous acid (HOCI) and hypochlorite ion (OCI). These two active chlorine compounds in water are called ”free chlorine”. Free chlorine is unstable, and reacts with organic material in the water thereby being reduced to chloride. Part of the chlorine reacts with ammonium compounds in the water and results in “bound chlorine”. The amount of organic material is normally higher in bunkered water, consequently requiring higher chlorine doses in order to disinfect the water.

Operation and maintenance The filter mass is constantly compressed, and consequently clogging the filter. The filter must be cleaned regularly by return flushing. Some substances in the mass do not dissolve, and are consequently accumulating in the filter tank. Some of these substances will be flushed out during the return flush operation, but after a while the tanks have to be emptied of these substances before refilling with new filter mass. Due to poor maintenance, micro-organisms might settle in the filter mass, causing high colony counts in the potable water tanks. The filter should be emptied before it is cleaned and disinfected at least once a year, like other parts of the potable water system.

8.1.2 Sodium Silicate

Chlorine inactivates bacteria by attacking the cell wall, penetrating the cell and destroying the enzyme systems. Virus is inactivated both by attacking

Adding sodium silicate reduces corrosion. Experience with sodium silicate is a bit mixed, but it can 42


the protein mantle, disrupting its ability to attack, and destroying the genetic material. As chlorine needs a certain time for these processes, the Pota ble Water Regulations requires a free chlorine level of at least 0.05 mg/l after 30 minutes of contact. Experience proves that it may be difficult to verify concentrations below 0.1 mg/l with the analysis methods used offshore. To achieve a best possible effect of the chlorine, it should be added as early as possible in the bunkering process. A chlorine amount of 0.3-0.5 mg/l might be sufficient for pure water, but if the bunkered water appears discoloured, a dosage above 1 mg/l may be required to achieve a sufficient amount of free chlorine. If free chlorine content above 0.05 mg/l after 30 minutes can not be confirmed, the water is not satisfactorily disinfected. The water must be re jected, unless the potable water system is equipped to mix in extra chlorine, see 7.3.3. How to calculate chlorine amounts, mixing of chlorine solutions etc., are described in appendix 11.

Figure 8.2: Water discoloured by humic material needs more chlorine than clear water to achieve a proper disinfection (Photo: Bjørn Løfsgaard)

Tests have shown that chlorine is 50 times more effective fighting bacteria in acid than in alkaline water. With a pH<7, the main part of the chlorine content is chlorous acid (HOCl), while the not so active hypochlorite ion (OCl -) dominates at a level of pH>8. Consequently, disinfection should be done before the water is alkalized.

8.2.2 Sodium hypochlorite

8.2.1 The significance of the water quality

Sodium hypochlorite (NaOCl) is sold in fluid form and therefore easy to use. Sodium hypochlorite has a limited shelf life, especially if exposed to light and/or heat, causing the active chlorine compound to break down and weaken its effect. If free chlorine is not found in the water after 30 minutes of treatment, the cause is often that the sodium hypochlorite solution is too old.

The colour of the water reveals a lot about the content of chlorine consuming organic materials (humic substances), though iron may also cause colour (figure 8.2). The chlorine dose needed to kill microbes must be increased in water with high content of organic material, in order to maintain the required chlorine level after 30 minutes of contact time. Generally it is sufficient to add 1 gram chlorine per ton (= 1 m 3), equivalent to 1 mg chlorine per litre.

In a newly mixed solution the concentration is usually 160-170 gram/litre, and is called 15 % solution. Because it breaks down during storage, it is safer to assume it is 10 % instead of 15 %. 15% sodium hypochlorite should not be stored more than 3 months after production date, but refrigerated it is good enough for 6 months. The lasting quality can be considerably increased by diluting the sodium hypochlorite with pure, de-ionised and distilled water. Some vendors supply such chlorine, and this chlorine may be stored longer.

To predict the amount of chlorine needed is often a greater problem for water works onshore than offshore, as water quality onshore fluctuates more than it does offshore. Offshore produced water needs less chlorine treatment, because the colour is checked already at the bunkering point and the water refused if the colour is unacceptable. In contrast to many other countries, Norway has a tradition of not accepting water tasting chlorine. The free residual chlorine in the water shall not exceed 0.5 mg/l after treatment, with the exception of disinfection of the pipe system, see chapter 9.2. Generally, the unpleasant smell of chlorine will intensify with increased amount of organic material in the water, as some organic/nitric chlorine compounds have a pungent smell and taste.

The chlorine solution can be added to the water without premixing, but if the chlorine pump capacity is good, it is preferable to dilute the solution, achieving a better control of the process. Sodium hypochlorite is a strong alkaline solution (pH 1011), and precautions have to be taken. It is particularly important to protect eyes and skin. Bottles with eye rinsing water should be kept within 43


chlorine will break down in about the same manner as sodium hypochlorite. For work environment, the same precautions as for sodium hypochlorite should be taken, see 8.2.2. Normally the chemical contains 60-65 % chlorine, but is often labelled with a content of 70 %. It contains 2-10 % insolu ble components, and causes sedimentation in the storage tanks. Such components, and should be separated before dosing, to prevent clogging of nozzles. Alternatively the suction hoses to the chlorine dosing pump could be lifted high enough to prevent suction of the bottom deposits.

8.2.4 Design § 11 in the regulations concerning mobile offshore units require that the chlorine dosing unit is permanently connected to the bunkering system, and it is favourable to have the dosing point located as near the beginning of the bunkering system as possible, in order to achieve best possible mixing. Figure 8.3: Flow meter controlled chlorination unit, safely placed in a cabinet (Photo: Bjørn Løfsgaard)

If chlorine is used for disinfecting produced potable water as well, the chlorine should be added before the water reaches the alkaline filter, since chlorine is most effective in acid water. It must be possible to add mix in more chlorine after finishing bunkering, and this is normally done through a circulation system.

reach. Clothes are also easily ruined by chlorine. Instructions should be carefully read and followed, such as wearing face protection, rubber apron, rubber gloves and other protective items suggested in the instruction data sheet. Accidents in operation of swimming pools have been reported, where sodium hypochlorite has been mixed with acid, forming chlorine gas, which is extremely poisonous. Such accidents are not known to have happened in connection with potable water, but it is advisable to be aware of the potential danger when storing and using such chemicals.

The unit should have short pipelines and hoses with small dimension from chlorine tank to bunkering pipeline. Chlorine pumps and tanks must have a capacity that corresponds with the chlorine solution volume to be used, and the dosing unit must correspond with the water quantities delivered by the supply vessel with the maximum pump capacity. The chlorine tank must be marked and leak proof, its water supplied from the potable water system, and have an easy to reach drain valve with a closed drainage system. If calcium hypochlorite is used, the tanks should be equipped with a stirring device to dissolve the powder.

Sodium hypochlorite can be produced by sodium chloride electrolysis (NaCl), so called electro chlorination. Several offshore units use electro chlorination on the sea water inlet to stop shell, plants and other marine growth. It is important to be aware of the fact that chlorous acid evaporates at a lower temperature than water, and will result in higher concentration in water produced in an evaporator. This can cause problems with taste, smell and unwanted by-products, see 6.2.

The best chlorine mixing is achieved if the speed of the chlorination pump is controlled by a flow meter, recording the speed of the water transferred to the storage tanks (figure 8.3). Experience with such controlled dosing is good, because it is easy to dose the correct chlorine amount into the entire water mass being bunkered. Chances for mistakes are reduced, as the chlorine dosing stops if the bunkering is interrupted. With a manually con-

8.2.3 Calcium hypochlorite Dry calcium hypochlorite (Ca(OCl)2) has an almost unlimited shelf life. Dissolved in water, the 44


trolled pump there is no such control of the chlorine dosing following the water bunkering flow. New units, and rehabilitation of existing units, should be designed with flow meter controlled dosing, see the Facilities Regulations § 19.

8.2.5 Operation and maintenance One advantage of chlorine disinfection is the sim plicity of the equipment. But even simple equipment may fail. This may be due to the corrosive effects of chlorine, or due to the thin hoses feeding the chlorine which may easily be squeezed thereby stopping the flow. The entire chlorination unit should be checked and cleaned regularly. The NIPH recommends that this is done at least every three months. If calcium hypochlorite is being used, sediment will form in the tank, requiring more frequent inspection and cleaning.

Figure 8.4: In unstable weather particles and sediments in the potable water tanks can be whirled up and sucked into the distribution system, reducing the effect of the UV-radiation. (Photo: Bjørn Løfsgaard)

of radiation. Fortunately, the atmosphere filters away UV-C and the greater part of the UV-B radiation. To inactivate microbes, a high dose UVC radiateon is needed. The UV-dose is a function of radiation intensity and time of exposure.

It is important to make sure that the pump suction is satisfactory, and that the chlorine does actually reach the water. It may happen that a pump only sucks in air only and not the chlorine. Necessary spare parts should always be available. Chlorine pumps are cheap compared to the consequences inferior chlorination might have, and an extra chlorine pump should always in stock.

Most offshore units use both chlorine and UV in their water treatment. One advantage of UV-disinfection, compared to chlorination, is that UV is more effective against some microbes like Giardia and Cryptosporidium parasites.

The following describes common causes when free residual chlorine is not present 30 minutes after bunkering is completed: • •

• • •

8.3.1 The importance of water quality Coloured and particle containing water can cause problems in the UV-disinfection, see 4.2.2, because the intensity in the chamber drops, thereby reducing the UV-dose. But coloured water can be disinfected by extending the radiation time. Particles in the water may “conceal” microbes. This is particularly problematic in offshore units if tank sediments are sucked into the potable water inlet (figure 8.4). Unstable weather conditions may also cause tank sediments to be whirled up. Exceeding the particle limit (turbidity above 1 FNU) must be avoided, and normally this is accomplished by installing particle filters prior to UV-units, see 8.4.

Defect pump/chlorine hose squeezed Too little chlorine added, see chlorine calculations in appendix 11 The sodium hypochlorite is too old Insufficient chlorine mixing Organic material content in the water too high

Some offshore potable water tests have shown free chlorine concentration way above the level of total chlorine. Such test results are not correct.

8.3 Disi nfecti on by UV-radiation Ultraviolet rays are part of the sun light spectre and are divided into UV-A, UV-B and UV-C radiation. UV-light is harmful to skin and eyes. Humans are exposed to UV from the sun and from man-made UV-sources like welding flames, solariums or UV-units. UV-C is the most harmful type

Chemical parameters such as iron and manganese may cause deposits on the quartz glasses reducing the UV-radiation intensity. The same may happen with calcium from the alkalizing filter. Regular cleaning is therefore important.

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Figure 8.5: This UV-unit has two radiation chambers, each chamber has a control panel (white) and an UV-sensor (on the front). The black valve closes if the radiation falls below the alarm level. (Photo: Eyvind Andersen)

Figure 8.6: The figure shows how average values for UV-transmission decrease as the colour number increases. The figure is based on water quality data from a large number of Norwegian water sources (Illustration: Karin Melsom)

8.3.2 Design, dimensions and approvals The UV-unit (figure 8.5) is the last treatment before the water is distributed. The NIPH certifies UV-units, see 2.3.4. This procedure ensures that minimum requirements to disinfection effects and control/supervision are fulfilled.

Type approval requires an UV-unit to be designed for maximum water supply and for the worst possible water quality regarding colour and turbidity. Maximum supply is normally much higher than the average water consumption, as the consumption varies. If pumps and piping systems can supply more water than the disinfection capacity of the UV-unit, flow restricting devices must be fitted.

When building new offshore units, and when replacing old UV-units, only biodosimetrically tested UV-units that give an UV-dose of 40 mWs/cm 2 should be installed. Such UV-units must fulfil strict design requirements, and such a high UVdose will also be a barrier against bacterial spores. Alternatively a barrier against such spores may be established through ultra filtration through mem branes with nominal pore openings less than 100 nanometres. Lists of approved UV-units that res2 pectively have an effect of 30 and 40 mWs/cm , are available on www.fhi.no/offshore .

The turbidity of water that is to be treated with UV must be less than 1 FNU. If higher turbidity values may occur, a particle filter must be installed. Turbidity problems may occur due to bunkering, change of tanks or corrosion.Most offshore units will need a particle filter in the potable water system (maximum pore size 50 micrometers). All offshore units may have to bunker water. Acceptable water from Norwegian water works may have colour up to 20 mg Pt/l. The UV-transmission (remaining UV-radiation after having passed through the water) of this water may be below 30 %/5 cm, see figure 8.6. When installing an UVunit, it is important to make sure that is has sufficient capacity even when the UV-transmission is less than 30%/5 cm. The list of approved biodosimetrically tested UV-units is supplied with information of which capacity each unit has at the lowest UV-transmission it is tested for. Unfortunately, only a few of the UV-units on this list have been tested at the low transmission values that may occur when bunkering Norwegian water.

For a type approval to be valid, the UV-unit must have at least two parallel radiation chambers, each must have enough capacity to disinfect 100% of the supplied water. With three chambers, each must cover at least 50% of the water. This arrangement allows safe water distribution, even when one chamber is out of use due to technical malfunctions, service or maintenance. If each cham ber has less than 100% capacity, the flow through each must be physically limited to the maximum capacity; having two 50% chambers in parallel operation is not safe unless the water is evenly distributed. 46


function, failure in one of the radiation tubes or, if the sensor indicates radiation intensity being too low. To ensure that enough disinfected is available at all times, the UV-unit should be connected to stable emergency power supply. Air inside the UV-chambers will reduce the effect. Gas traps must be avoided through having high point vent possibility for each chamber and by placing the outlet level to or above the inlet. Test taps fitted just before and just after the UV-unit may be used to verify that the disinfection is functioning (figure 8.6). Figure 8.6: UV-unit with test taps before and after disinfection (Photo: Eyvind Andersen)

8.3.3 Operation and maintenance UV-units should be supervised daily. If the alarm is connected to a manned control room, physical supervision can be reduced (figure 8.7). Every control should be logged and information recorded, describing corrective actions taken.

By dimensioning the UV-unit for the poorest quality of bunkered water, one will have much redundant disinfection capacity for produced water. This may also result in an unwanted increase in water temperature, but may be avoided through several measures, for example by having a 3*50% capacity UV-unit, where only one is used for produced water, if this gives sufficient effect.

Never expose eyes and skin to such UV-light without protection. S ymptoms usually occur a few hours, and such injuries have happened on offshore units. Blurred sight and the feeling of sand in the eyes are minor reactions, but temporary or permanent blindness, may be the consequence.

Figure 8.6 shows average values for Norwegian water. The real UV-transmission of bunkered water of acceptable colour may be significantly lower. To compensate for this, it is possible to use all chambers in parallel when measurements of bunkered water show values near the colour limit.

Written operating instructions should describe maintenance routines such as cleaning instructions and how to change tubes. Maintenance procedures given by the supplier should be followed. Minimum maintenance frequency for vital functions should be as described below:

To avoid overheating and shutting of UV-units, the suppliers recommended minimum water flow must be met at all times. One recommended solution to achieve this is to design the potable water system with continuous pumping of water, with a return line to the tanks connected after the UV-units. If consumption is low, a pressure valve opens, and the water is automatically returned to the same tank it was supplied from, see figure 5.1. Each UV-chamber must have a sensor for intensity monitoring and an alarm signal in case of low intensity or malfunctioning radiation tubes or power supply. Each UV-radiation tube shall have an alarm light showing that it is functioning. A timer for each unit shall log hours the radiation tubes have been in operation.

Figure 8.7: An UV-unit control panel. The blue light indicates that radiation tube number 2 is in operation and functioning. In the centre of the picture you can see a hour counter (black) and an UV-intensity meter (Photo: Eyvind Andersen)

Each UV-unit shall have a solenoid valve closing the water distribution in case of electrical mal47


Intensity meter If the unit is not equipped with an automatic alarm system, the UV-intensity meter should be read daily. The intensity meter and alarm set-point should, as a rule, only be adjusted by the supplier/producer. In agreement with the supplier/ producer adjustments may also be made by specially trained personnel with calibration knowledge. Calibration is normally done once a year. For the biodosimetrically tested UV-units calibration is easy, as the type approval demands that such units use standardised UV-sensors that may be replaced by reference sensors.

three months. If the system is equipped with automatic mechanisms for cleaning (brushes, rubber rings or equivalent) the effectiveness must be checked and the equipment cleaned at least every six months. If the water contains iron or manganese, this might scorch the quartz glass. The scorching is normally removed by acid washing, but in some cases it is necessary to scrub by hand. Spare parts The unit shall have the necessary spare parts for continuous operation including radiation tubes (a complete set), quartz tubes, packing material, radiation tube relays, fuses, ignition charge and light bulbs for the indicator lamp. Spare parts for the UV-intensiometer and the alarm system should also be available.

Low UV-intensity found and the cause corrected without delay. If it is due to sedimentation on the tubes or sensor eye, the entire inside should be cleaned. Other elements in the system should be checked as well. If the intensity of the radiation tubes is too low, the tubes should be replaced. Low intensity can also be caused by inferior water quality. This may happen after bunkering or in connection with switching of storage tanks.

8.4 Active carbon fi lters

Carbon filters solve certain water quality problems by efficiently removing substances present in the water due to pollution. Such substances often cause unpleasant smell and taste, and may be hazardous to the health, see 4.2.1. Nevertheless, the need for carbon filters point towards sub-standard operation or unfortunate technical solutions, and therefore ought to be unnecessary. Carbon filters are efficient in treatment of unpleasant taste and other problems caused by for example:

Signal lamps, radiation tubes and hour counter Hour counter and signal lamps for UV-radiation tubes should be checked weekly. The UV-radiation tubes should be replaced before the radiation effect is reduced by 20-40 %, when maximum operation time has been reached, and also according to the supplier’s special recommendations. Normal operation time for low pressure tubes is 8,000 hours and 3,000 hours for medium pressure tubes. If the UV-unit has several radiation tubes in each chamber, they should all be replaced at the same time, to maintain control of the chamber intensity. The exemption to this rule is a radiation tube that malfunctions shortly after being replaced. But at the next time of replacement all radiation tubes should be replaced, including the newly replaced radiation tube.

• •

• •

Chlorine Chlorine by-products for instance trihalomethanes Waste product from algae Soluble products from protective coatings in the potable water storage tanks

Continuous maintenance of the filters is vital for the effectiveness, but also because bacteria might develop in the filter due to good growth conditions resulting in high colony counts. Today, most filters are delivered with filter material in a cartridge. Since the filter binds the chlorine, it must be removed in the yearly pipeline disinfection and be replaced according to recommendations made by the supplier. With the probability for bacterial growth, the filter should always be placed prior to the UV-unit. Some carbon filters also function as particle filters, and such filters may replace ordinary particle filters prior to UV-units.

NB: The type approval of UV-units is only valid when using radiaton tubes of at least the same effect as the ones that were a part of the type approval application. If type of radiation tube is changed, the effect must be sufficiently documented. Cleaning The radiation chamber (such as quartz pipes, sensor eyes, reflectors) must be cleaned regularly, depending on water quality – minimum once eve-

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9. Storage tanks and d istri butio n sy stem Bunkered or produced potable water will, after treatment, be stored in water tanks and from there passed on to the consumers through a distribution system. Hydrophore tanks, day tanks etc. are also regarded as potable water tanks.

may be even further reduced if several storage tanks are used. Offshore units without potable water production onboard should have a least three storage tanks. A unit with only two storage tanks can not bunker water according to the requirements if one tank is out of operation. It is required that the storage tank being bunkered to should be isolated until free residual chlorine is documented 30 minutes after bunkering is finished. Consequently, with only two tanks aboard, there is no tank from which water can be distributed, when one tank is out of operation.

9.1 Potabl e water t anks

Offshore units are required to have a sufficient amount of potable water aboard, and the tanks must be operated separately to avoid simultaneous pollution of all tanks. The necessary number of storage tanks and total storage capacity depends on production capacity and demand. The minimum requirement is 200 litres per day per person. Storage tanks with an unsuitable design may require increased maintenance and maintenance costs, and may also result in inferior water quality.

Problems with insufficient storage capacity usually arise when one tank is being cleaned, and this risk increases if a new coating has to be applied. This means that one storage tank will be out of operation for several days and, at the same time requiring large amounts of water for the maintenance process. Occasionally storage tanks are out of operation for several weeks following maintenance work because the hardening process has resulted in problems with smell and taste. Sudden contamination of a potable water tank may also leave the tank out of operation. In table 9.1 a minimum storage capacity is recommended for the various unit types.

9.1.1 Storage capacity The owner shall be able to document that sufficient hygienically safe potable water can be supplied under any circumstances. The amount of potable water to be stored depends on how vulnerable the water system is. A potable water system exclusively depending on bunkered water is vulnerable because bad weather conditions may make bunkering impossible. The quality of bunkered water is often unpredictable and consequently requires a larger storage capacity. Units that, in addition to bunkering, produce water are less vulnerable, and two or more production units will strengthen the safety. Minimum storage capacity is reduced for such units, and

Under normal circumstances the potable water unit should be operated so that water is not stored in the tanks more than 20 days. This will prevent problems with smell or taste caused by the tank coating or decomposing of organic material.

Table 9.1: Guide to minimum total storage capacity specified in number of consumption days. Each tank is presumed to have equal storage capacity. Recommended total storage capacity for: Number of storage tanks 2 3 or more Unit based on bunkering only Not recommended! 20 days capacity Unit with one production unit with 100 % capacity plus 20 days capacity 15 days capacity bunkering Unit with two production units with 50 % capacity each 15 days capacity 10 days capacity plus bunkering Unit with three production units with 50% capacity or 8 days capacity 5 days capacity two units with 100 % capacity each plus bunkering

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products than potable water are not accepted in a potable water tank, but if this is necessary, these pipes shall be carried through open ducts. The water storage tanks shall be fitted with sufficient ventilation, test taps, manholes, levelling meter, drainage, and be protected against frost and heat. Potable water inlet and outlet

The inlets for both bunkered water and return water from the distribution network should be located away from the outlet, to enhance water circulation in the tank. The high pressure of bunkered water should also be utilized by pointing the inlet in angle that increase the circulation of the full tank volume (figure 5.1). This will prevent pockets of stagnant water and improve the mixing of chlorine in the tank. The potable water outlet shall be placed above the bottom level of the tank to prevent sediments from entering in to the water distribution system. Sediments may carry bacteria through the UV-unit and may also cause operation problems with the UV-unit, pipeline system and filters.

Figure 9.1: A 12 meters high tank has been split into 4 meter compartments to make maintenance easy. Vertical stiffeners are easy to high pressure clean standing on the tank floor. Between com partments the openings are secured (though more openings would have been advisable to avoid stagnant pockets). Circulation is achieved by placing the inlet in the upper compartment and the outlet in the bottom one (Photo: Eyvind Andersen).

9.1.2 Design and location The Facilities regulations §§ 4, 9 and 19 give general requirements for system design, and the following advice is based on these requirements. The inside of a potable water tank should be as smooth as possible, without nooks and corners that may harbour microbes. Frames and other constructions breaking up the interior should be avoided since this may form ”pockets” of stagnant water not being reached by the disinfectants, creating opportunities for growth of microbes. Large inner surface, compared to volume, have created problems with smell and taste after protective coatings have been applied, see 9.1.4. According to the working environment considerations, water tanks should be designed to make maintenance work comfortable and to be carried out in an upright position without scaffolding, see figure 9.1.

Air vents

Potable water tanks shall be vented to the open air or a non-polluted area. Normally it is sufficient to have one air vent connected to each storage tank but, if the tank has separate, closed sections, each section has to have an air vent. The opening must be protected against sea water, birds and other substances that might contaminate the water (figure 9.2). The opening shall be covered by a fine meshed net of a non-corrosive material.

Potable water storage tanks should be placed where they are not heated from the surroundings, neither sun nor any other source. Water temperao ture should be kept below 20 C, even during the summer season. To avoid contamination of all potable water onboard, the storage tanks must be separated from each other to prevent possible contamination of one tank from spreading to the other storage tanks. Potable water tanks shall not have joint walls with tanks containing petroleum products, liquid chemicals etc. Pipes transporting other

Figure 9.2: Pieces of a dead bird found in a potable water tank. The bird entered via the bunkering pipe, was caught in a valve and spread to all water storage tanks as the body decomposed (Photo: Anonynous)

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Drainage The storage tanks should be equipped with sufficient drainage facilities. Cross braces shall have openings near the tank bottom to enable total drainage. The tank bottom should be sloped or supplied with a pump well leading the water towards the drainage point (figure 5.3). The drain valve should be placed at the lowest point. If the tank bottom construction does not allow “natural” drainage, a permanent pump should be installed. Unfortunately storage tanks are often built with a flat bottom and without a pump well. Draining of storage tanks is therefore frequently done by using the potable water pumps, which is unfortunate if a tank is drained because the water is contaminated.

Access possibilities A storage tank has to be equipped with a manhole to facilitate inspection, cleaning and maintenance. Generally one manhole is sufficient, but two may give better access and ventilation possibilities. To avoid contamination of the tanks the manholes should have close-fitting covers.

The manhole must have a size and location that provides easy access to the tank for both workers and equipment (figure 9.3). Some storage tanks have tank roofs as part of the deck. Manholes on deck should have a rim minimum 5 cm high, and be located in a ”clean” area. Water gauge The water gauge system should be automatic. Water quantity in the storage tanks will then be constantly monitored from the control room, activating an alarm if the water level becomes too low. Visual control is still used on some older offshore units, but use of dip stick is not acceptable.

Water for flushing Potable water tanks are often cleaned by use of high pressure water, and this water should be of potable water quality. Test tap A test tap should be fitted to facilitate testing of chlorinated water in the tank without having to lead the water into the distribution net.

9.1.3 Operation and maintenance During operation, deposits of organic material, rust particles etc., will settle on the tank bottom, becoming an ideal growth environment for microorganisms. A thin film of organic material will form on the tank walls, where organic material will adhere and bacteria grow. The storage tanks have to be cleaned and disinfected at least once a year, or more often if necessary. Experience with potable water tanks receiving bunkered water only, indicates that cleaning at least twice a year is necessary, while once a year often is sufficient if the potable water is produced onboard. If water storage tanks are not cleaned often enough, it will be difficult to remove the growth. Following any type of maintenance work, tanks must be disinfected. Hydrophore tanks, day tanks and distribution reservoirs all require the same cleaning and disinfection procedures. The procedures are described in appendix 13. Cleaning and disinfection have to be carefully planned. Storage capacity of the tanks in use should be fully utilized. During maintenance it is not unusual that a tank is out of service for several days. If a new surface coating is needed, it may take even longer before the tank is ready for use again. The water quantity needed, hardening time and other requirements, such as manpower, ne-

Figure 9.3: The picture shows a storage tank with easily reached test tap and an accessible manhole (Photo: Eyvind Andersen)

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cessary water production etc. should be considered in planning the maintenance work. Maintenance, such as renewing the coating, is best done during the summer months, when the weather is good and hardening time shortened.

that may be applied and cured under the local conditions will be used. After the tank has been coated, it should be verified that these conditions have been fulfilled, and as a check, the water in the tanks should be verified for hydrocarbons, see appendix 13.

During tank inspection the cleaning intervals should be carefully considered. If the tank bottom sediments are negligible and the colony count steady and low, cleaning intervals are satisfactory. The storage tanks must not have any substantial corrosion damage. The water gauge, air-vent net and float should be inspected. The inspection results shall be logged.

9.1.4 Smell- and taste problems due to protective coating

Figure 9.4: Picture of a storage tank with newly applied protective coating. In a tank with a large inner surface compared to volume, the risk for growth of micro-organisms increases, as well as problems with unpleasant smell and taste (Photo: Eyvind Andersen)

Potable water with an unpleasant smell and taste, following protective coating inside a storage tank, is unfortunately a common problem on offshore installations. Some substances causing the water to smell and taste unpleasant, are hazardous to the health, and water with smell and taste may not be used for human consumption, see 4.2.1 and 4.3. Active carbon filter has proven effective in removing these substances, see 8.4.

9.2 Water dis trib utio n sys tem The water distribution system supplies water to living quarters, galley and other areas on the unit, and may consist of feeding pumps, day tanks, pressurizing systems, hot water system, valves and pipe lines. The system is pressurized by continuous pumping, or by pumping water to the distribution reservoir or to a hydrophore tank.

Problems often occur because of inappropriate application of the protective coating, and/or an insufficient hardening process see certification requirements in chapter 2.3.4. Applying the protective coating too thick or using thinners or wrong application routines can cause problems. Insufficient hardening is often a result of not following the producer’s suggestions regarding hardening time and temperature. Several certified products are not suitable for use offshore during operation, since hardening requirements will be impossible to adhere to because of low temperature, cold steel and short deadlines.

Experience indicates that a unit may have inferior potable water quality because of weak points in the water distribution system, for example poor quality pipes or pipes not designed for that particular water quality. If the water distribution system is not sufficiently protected against contamination from other systems, this may also result in undesirable water quality and it is strongly recommend that such weak points are avoided. Systems not carrying potable water, can by mistake, be connected to the potable water system if the water distribution system is not clearly marked. Having a properly marked water distribution system also makes it easier to follow the pipe lines in a critical situation, when it is important to be able to quickly locate a malfunction.

The location of the storage tanks may in itself cause hardening problems. If the tanks are ex posed to weather and/or are poorly insulated, the outer walls will still be too cold in cold weather, even if the inside of the tanks reach the correct hardening temperature. Consequently only the surface part of the coating hardens properly. This situation may cause volatile substances to seep into the water for a long time, see figure 9.4. For newbulds, repairs and offshore tank maintenance one must in advance make sure that only coatings 52


By having two or more potable water tanks, the system is equipped to deal with pollution, on the condition that the tanks are operated separately. If the system is designed with a return line to the tank, automatic valves can make sure that the water is returned to the same tank that it was pumped from.

provide sufficient minimum flow through the UVunits and extra water disinfection. The pumps should not have a particularly large capacity since excess heat can increase the potable water temperature, see 4.2.5.

9.2.3 Design of water distribution systems When planning or rebuilding a unit, the water distribution system should be carefully assessed. Materials that come into contact with potable water shall not give off substances to the water in such quantities as to make it hazardous to health or unsuitable as drinking water.

9.2.1 Pressurizing with hydrophore units or day tanks A hydrophore unit consists of a pressure pump and a hydrophore tank. The hydrophore tank normally holds 1-5 m 3. The pump is controlled by the water level in the pressure tank. Air pressure controls the amount of air in the hydrophore tank. The pressurized air must not contain any oil traces, and must be filtered if there is any sign of such substance being present. A membrane tank can alternatively be a functional solution.

Blind pipes and pipes with more or less stagnant water should be avoided since that water will maintain room temperature and gather contaminants. Bacteria growing in blind pipes will not be reached by disinfectants during the yearly disinfection, resulting in microbes re-spreading throughout the distribution system. Pipe ends that are longer than 10 times the pipe diameter are considered “blind”, and should be removed.

Some systems are equipped with elevated day tanks to make distribution by gravity possible. The day tanks can be equipped with a float that starts and stops the pump depending on the water level. The volume is fairly small with a normal storage capacity of less than 1 day of consumption. The same design and operation requirements apply as for other types of storage tanks. With only one day tank, it has to be designed with a by pass possibility to allow for regular cleaning and maintenance without interrupting the water distri bution. Hydrophore tanks and day tanks save energy as pumps run only when tanks are being filled. The water flow through both hydrophore tanks and day tanks is considerable as the volume in the tanks is rather small compared to wall and floor surfaces. This leads to more nutrients being available for bacterial growth on walls and floor, requiring more frequent cleaning compared to larger tanks with less water flow.

The cold water temperature should not be above 20oC. Cold potable water tastes better and it is therefore recommended that the temperature is kept even lower. Potable water pipes in rooms with high temperature should be insulated. Outdoor piping should be insulated against frost and heat and should not be exposed to direct sunlight. If the cold water temperature is too high, a heat exchanger should be installed to effectively cool the potable water. If exceptionally long pipelines supply coffee makers and water coolers etc., such equipment should not be connected directly to the potable water system, because the copper content in the water can become too high if there is no possibility to flush stagnant water.

9.2.2 Pressurizing with pumps

Both for newbuilds and repairs it is important that the pipeline material chosen withstands the particular type of water quality (figure 9.5). Such a recommendation might seem unnecessary, but experiences from offshore units being built or refitted recently, have revealed that choosing the wrong type of pipe material have caused instant corrosion problems. To replace the entire potable water system or parts of it, often represents a substantial extra cost.

The water can also be distributed with the help of pumps. Generally a system will have two pumps, one being in operation and the other as a stand-by pump. Pumps should be operated from a centrally located control room. A recirculation pipe line going back to the distribution tank should always be installed. This pipe line feeds a small return stream in order to prevent the pump from overheating during periods of low consumption. If this line is connected after the UV-unit, it may also 53


changer have to be certified by the NIPH, see 2.3.4. Metals (copper) will always corrode quicker in a hot water system consequently hot water pipes shall never be connected to installations in the kitchen where food is prepared. The hot water distri bution system must also be equipped with backsuction valves just like the cold water system. Research has proven that certain patogenic bacteria will grow in hot water systems maintained at too low a temperature. The Legionella bacteria in particular can cause problems if the water is not kept hot enough. If the water in the hot water distribution system maintains a temperature of at least 60o C following one minute of flushing, the chances for infection is minimized, see 9.2.7.

Figure 9.5: Pipes and valves in potable water systems vary in size and material. It is important that corrosion resistant materials and materials that do not encourage bacterial growth are chosen (Photo: Eyvind Andersen)

The most common pipe material used in water distribution systems offshore is copper in the living quarters and stainless steel in the rest of the unit. Occasionally hard plastic is used in living quarters. Metal pipes may be susceptible to corrosion, but are generally easy to work with and resistant to pressure damage. Titan and acid resistant stainless steel are eminent corrosion resistant pipe materials, and are therefore used in pipes that are particularly exposed to corrosion such as sea water pipes and pipes between water production unit and alkalizing filter. Hard plastic does not corrode, and leakage of unwanted substances is seldom a problem. Hard plastic pipes have limited mechanical strength, and should not be used in installations outside living quarters. Under certain circumstances plastic piping might cause bacterial growth in the distribution system.

9.2.5 Protection against pollution The potable water must be safeguarded against pollution. Consequently the distribution network must be evaluated with regard to possible sources of contamination, and necessary protective measures must be applied. More information on this is available in Norwegian Standard ”NS-EN 1717”. The best way to protect the potable water system is to make sure that it is physically separated from potential sources of contamination. This is achieved through having a separate system for process water, or by separating connections through a complete air-gap, a so called “broken connection” between the potable water system and possible sources of contamination that are supplied with potable water. The air-gap must be at least 20 millimetres and at least 2 times the pipe diameter (measured between the bottom of the potable water tap and the highest possible water level in the connected equipment. Such a connection is according to level “AA” in the standard).

9.2.4 Hot water systems Hot water being used in sanitary units (showers and sinks) has to be of potable water quality. The hot water system must be connected downstream of the disinfection unit. The connection has to be secured against back-suction of hot water to the cold water system, see 9.2.5. It is important that the hot water pipes are insulated, or placed away from the cold water lines to avoid warming of the cold water during transport through the pipe system.

Some times it is difficult to achieve “broken connections” between the potable water system and all technical systems supplied with potable water. In such cases other technical solutions may be evaluated to prevent back-flow due to suction from the potable water system or pressure from the technical connections. When such barriers are applied, it is important that that it is possible to test that they are functioning correctly, and procedures for regular tests must be in place. Which

Water is normally heated by electricity, but some units use surplus heat from cooling water or steam passing through a heat exchanger. Chemicals being added to the water or steam in the heat ex54


barrier is chosen depend on the level of threat each connection poses, and the greater the risk and/or consequences are, the greater safety requirements are.

9.2.6 Operation and maintenance The main problem with biofilm (bacteria and other microbes) in the potable water distribution system is that it can suddenly give the water an unpleasant smell and taste, see 4.2.1. Some of the bacteria may also be pathogenic, and underneath a biofilm pitting may begin, see 4.2.3.

The second best level of technical safety is achieved by fitting a Verifiable Reduced Pressure Zone (RPZ)-valve (level “BA” in the standard). A RPZ-valve consists of two non-return valves separated by drain chambers (figure 9.6). The drain chamber pressure will never be higher than the up-stream pressure, and the chamber will be drained by a drain valve that opens if failure due to back-suction or back pressure occurs. A RPZvalve is the only form of protection that is recommended for permanent technical connections to the potable water system and for connections supplying sprinkler- and hot water systems.

It is a common misunderstanding that disinfection of the water distribution system is to be done only if there are plenty of bacteria in the water. Disinfection of the distribution system shall be carried out regularly in order to prevent forming of biofilm. It is more difficult to succeed with disinfection if a biofilm is already present, and the disinfection process might have to be repeated several times to remove the bacteria. A clean water distri bution system is relatively easy to disinfect, and smell and taste of chlorine will soon disappear.

Verifiable non-return valves (level “EA” in the standard) represent the lowest level of safety that should be applied offshore, and should only be used if there is little risk of pollution and the consequences of malfunction are acceptable. After a thorough evaluation such valves may be fitted on hose connections (depending on where the hose may be used) and pipes supplying washing machines etc. (such connections must also be protected by locating the connection above the fluid level, which is generally done in new machines).

Cleaning and disinfection of the distribution system has to be done at least once a year (the Activities Regulations § 11 referring to the Regulations concerning potable water system and potable water supply on mobile offshore units). The Regulations state that “tanks, pipes and pipe systems for potable water shall at all times be kept clean on the inside all the way to the tapping points. Cleaning and disinfection of the entire potable water system shall be carried out before the unit leaves the yard, after repairs, and then at least once a year”. It is important to notice that the Regulations say at least once a year, and that it has to be cleaned and disinfected more often if necessary. Cleaning of the distribution system is also recommended in connection with disinfection of one or more storage tanks, see chapter 9.1.3).

Only technical barriers whose effect may easily be verified should be applied offshore.

Increased colony counts indicate a need for cleaning and disinfection regardless of the planned maintenance intervals. Colony counts above 100 (at 22o C/72 hours) in two consecutive tests indicate the presence of biofilm in the distribution system. It is easy to make mistakes in testing and perhaps contaminate a test. This is eliminated by taking two consecutive tests. Another test should be taken as soon as possible if one test shows sign of increased colony counts, and if this is a fact, remedial actions have to be taken. Flushing the system should be the first remedy to be tried. If the colony count does not decrease or soon increases again, the entire distribution system should be

Figure 9.6: Other liquid carrying systems should not be supplied with potable water. If this can not be avoided, broken connections or double backsuction/back-flow protection, with drainage between the two systems, will give the best protection against contamination (Photo: Eyvind Andersen)

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flushed once more and disinfected. The cleaning and disinfection procedure is described in appendix 12. To ensure that the entire distribution system is sufficiently chlorinated is a major undertaking and is often dele-gated to external consultants. Shower heads and shower hoses often contain a great deal of biofilm, and are difficult to disinfect sufficiently. They should be dismantled, cleaned and disinfected regularly, see 9.2.7.

•

•

•

The water temperature should be reduced to below 30o C when disinfecting the hot water system with chlorine. Alternatively the hot water system may be disinfected by increasing the temperature in all o of the distribution system to 70 C for at least 5 minutes.

the coldest point in the pipe system after one minute of flushing. Normally the temperature in the hot water tank should be at least 70 o C (figure 9.7). Blind pipes are removed from the potable water system, see 9.2.3. The potable water distribution system is cleaned and disinfected regularly, see 9.2.6. Shower hoses and heads are especially difficult to keep clean, and every 3 months these fixtures should be disassembled, cleaned and disinfected by heat, drying or use of disinfecttant, see appendix 12. After a period without use of the showers, it is such disinfection is even more important.

For more information on legionella, including the latest about legionella prevention, please see the NIPH guideline in legionella prevention (only in Norwegian language), which the above recommendations have been based on.

If the potable water distribution system is connected to other systems as mentioned in chapter 9.2.5, it is of utmost importance that back-suction valves are kept under surveillance and regularly tested. Back-suction valves have to be replaced according to the producer’s recommendations. Pumps and other equipment should also be maintained in accordance with recommendations made by the producer, and in addition, disinfected at least once a year along with the rest of the potable water system.

9.2.7 Legionella prevention Legionella growth normally occurs in potable water systems with temperatures between 20 and 50o C, and regular disinfection routines are lacking, see 9.2.6. Breathing in aerosols (micro sized water drops) emitted from for example aircondition units or showers can, under certain unfortunate circumstances, result in two types of sickness. Legionnaire’s disease is a very serious type of pneumonia with high mortality. Pontiac fever is normally quite like influenza. The following measures will reduce the risk of legionella growth in the potable water system: •

Figure 9.7: Problems with Legionella bacteria growth is avoided by keeping the hot water temperature high (Photo: Eyvind Andersen)

The cold water temperature should be below o 20 C, and the temperature in the hot water system should be kept above 60 o C, measured at

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10. Water supply on diving vessels – special requirements Diving vessels are vessels equipped with units for deep diving operations. These vessels are often in operation close to other units where divers perform construction and maintenance work. The work periods will last up to 3 weeks and include compression, actual operation time and decompression. During this time the divers live in compression chambers onboard the diving vessel when they are not working from diving bells in deep water. The compression chambers are closed systems where contamination may accumulate and where traditional medical treatment cannot be easily executed, making it particularly important to ensure safe operations (figure 10.1). The NORSOK U100 guide describes the special requirements for potable water distribution systems on diving vessels.

10.1 Water analyses The Potable Water Regulations apply to ships as well. The recommended analyses in chapter 4, made by the NIPH, apply to diving vessels as well. Additional operation analyses for P. aeruginosa should be taken of the diving system on the vessel, before operation starts and then at least monthly during operation periods. In both the ordinary potable water system and the diving system 500 ml tests of the cold water (cw) plus the hot water (hw) should be taken at the following test points: •

• •

This chapter covers challenges that are special for diving vessels. The general requirements for potable water described in chapters 1-9 will in some instances not be pertinent because diving vessels have different requirements than other offshore units. For instance will the requirements for training of personnel have to include the special considerations that are necessary on diving vessels.

•

•

Mess: cw (only when the diving system and the rest of the vessel share the water distri bution system) Diver’s kitchen: cw and hw Room for rinsing diving suits: cw and hw Showers in the diving system chambers: cw and hw from each chamber Cold water/ and hot water tanks supplying the diving system

Even though monthly analyses normally will be sufficient, according to the experience of the diving companies, the frequency will have to be increased when for instance P. aeruginosa is found. For units that repeatedly experience infections among divers, increased analysis frequency should always be considered.

Divers also need hot water to keep the diving suits warm in the cold sea water. For this pur pose heated sea water is used, but this is not discussed in this guide.

10.2 Water pro duct ion

Living quarters and work environment for divers have been studied in a medical research program carried out by Statoil, Norsk Hydro, Saga Petroleum, Norske Esso and the Norwegian Petroleum Directorate. Divers often have skin infections, and Pseudomonas aeruginosa is almost always the cause. The bacteria are common in both salt water and fresh water. The main reservoir for such bacteria in the diving system is the potable water, where infection may spread through showers and other use of the water. A few genotypes of P. aeruginosa are predominant in the infections, and those genotypes repeatedly appear in disease outbreaks. Regardless of which type of P. aeruginosa being present, curative actions should be taken. SINTEF Health keeps a database of North Sea genotypes.

It is recommended that the water supply in the diving unit is based primarily on production aboard and not by bunkering water delivered from ashore. This is preferable because: •

•

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P. aeruginosa cannot pass through either an evaporator or a reverse osmosis unit, as long as these are operated correctly. Bunkered water may contain P. aeruginosa. P. aeruginosa grows faster when pH is around 8. Produced water that is not alkalized holds a pH below 6. Feeding the diving system with this type of water will also limit growth of P. aeruginosa. Bunkered water and alkalized water normally hold a pH between 7 and 9.


Disinfection units The diving system should have a system for chlorination of the storage tanks, and possibility to increase the chlorine concentration by circulation. Two parallel UV-units with particle filter in front should be installed, as close as possible to the pressure chamber.

10.3 Design The following criteria should be considered in the design and construction of a diving system: Separate closable sea water inlets, see 6.1.2. Suitable pipe material Non- alkalized water produced aboard is very corrosive, and a suitable quality material must therefore be used. Titan is the best material and highly recommended. Hard plastic material is sometimes suggested because of its resistance to corrosion, but should be avoided because P. aeruginosa is a bacteria that easily forms biofilm on plastic material and may “feed” on PVC.

10.4 Maintenance When the diving system is not in use, the water storage tanks and the pipe system should be drained. Before the storage tanks are filled up again, they should be cleaned and disinfected, see appendix 13. If the diving system is in use often, it may be sufficient to disinfect the storage tanks twice a year. Before the pipelines from the tanks are ready for use, they should be disinfected with chlorine dioxide. This method is effective and inexpensive, and does not influence the rest of the potable water system on the unit.

Dedicated tanks Recommendations for non-alkalized water being produced onboard require separate potable water storage tanks for the diving system. The water is lead directly from the production unit to these tanks, and consequently, does not pass through the ordinary potable water tanks. This solution has the advantage that water from the regular potable water tanks, potentially contaminated by P. aeruginosa from bunkered water, is not fed into the diving water system.

If the water analyses show growth of P. aeruginosa, the infected parts of the system must be cleaned and disinfected. If the growth is located within the diving system, the same procedures as described above should be used. If the growth includes the entire potable water system, procedures described in appendices 12 and 13 apply.

Diving vessels often operate close to other units, making it difficult to produce water. To avoid using bunkered water in the diving systems, it is preferable to have storage tanks with enough capacity to ensure an adequate water supply.

Suggested procedures for water production on board the units to dedicated storage tanks, and routines for disinfection of the storage tanks and pipelines, are given to prevent growth of P. aeruginosa, but are safeguarding against Legionella pneumophila as well.

Figure 10.1: Pressure chamber designed for diving operations (Photo: Eyvind Andersen)

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App endi x 1 – Check list for design of potable water systems on offshor e units Name of unit: Type of unit: Delivery date: Bed capacity: Maximum number of people aboard: Official contact person(s): Owner(s)/operator(s):

1. Preface This check list is meant as a tool for the planning and construction of potable water systems on offshore units, and should be included in the documentation submitted to the authorities when potable water systems are being built. The check list should also be used in the planning of major changes of existing potable water systems. The items in the check list are in accordance with Norwegian Regulations and the guideline issued by the Norwegian Institute of Public Health (NIPH), but there may be other acceptable alternatives to the solutions listed here. The check list is general, and there will always be items not covered by this list, but nonetheless should be considered during the planning and construction. The owner/operator is responsible for building and operating the potable water system and delivering sufficient and satisfactory potable water according to the Regulations.

2. Rul es and gui delines The persons responsible for planning and construction of the potable water system should be familiar with the contents in the following Regulations and guidelines: Regulations of 31 August 2001, relating to health, environment and safety in the petroleum activities (consisting of the HSE Framework Regulations with subordinate regulations) Regulations of 4 September 1987, no. 860 concerning potable water system and potable water supply on mobile offshore units Regulations of 4 December 2001, concerning potable water The NIPH guideline ”Sufficient, safe and good potable water offshore”

3. Important decisio ns duri ng early con ceptual phase When building a potable water system, many important decisions are taken in the early planning stages. Our experience is that the best offshore water systems consist of the following units: Two sea water inlets located at a safe distance from the unit’s discharge points, ref. item 5 A sea water system where the first tapping point after the inlet is the outlet to the production unit for potable water. Subsequent connections to the sea water system must be equipped with backflow/back-suction valves to prevent contamination, ref. item 5 At least two water production units (evaporators or reverse osmosis units), ref. item 8 Alkalizing filter, ref. item 7 Two bunkering stations placed on opposite sides of the offshore unit, ref. item 8 Permanently installed chlorination unit (s), connected to the filling and recirculation pipes for the potable water tanks, ref. item 9 At least two potable water storage tanks with enough capacity, designed to facilitate maintenance and placed to avoid warming of the stored water, ref. item 10 At least two UV-units, ref. item 11 59


In addition to choosing type of units to be installed, the following must be clarified during the early design stage: 3 Maximum amount of potable water required (at least 200 litres/person/day) m /day:____________ Maximum need for water supplied from the potable water system for purposes other than domestic (i.e. technical connections to the potable water system):________________ A potable water system completely separated from the technical water supply system Experienced personnel have used 3D-verification of drawings to ensure that all components in the potable water system requiring regular maintenance or service, are easily accessible and ergonomically designed, including: Bunkering station Chlorination unit Potable water tanks UV-units Water maker Alkalizing filter CO2-unit Other water treatment units Manually operated valves

4. The pot able water syst em in general The potable water system has been evaluated and measures taken to safeguard against human errors An analysis of the risk/vulnerability has been conducted for the potable water system All chemicals added to the potable water, or chemicals that may contaminate the system through leakage, maintenance work, back-suction etc., are certified All drawings are easy to understand and include the entire potable water system, as well as other systems connected to the potable water system An internal control system is established, certifying that the potable water system is built according to drawings and specifications

5. Sea water in let and sea water sys tem There are two separate sea water inlets that may be operated separately The sea water inlets are placed separated from each other both horizontally and vertically to ensure that one inlet can operate should the other be polluted The spreading pattern of discharges from the unit has been calculated in relation to positioning the sea water inlets to secure a minimum of risks of pollution via the sea water inlets If electro chlorination is used to prevent marine growth from blocking the sea water inlet, this system will at all times be operated without any risk of unacceptable levels of chlorine and bromine compounds after an evaporator

6. Water production syst em The water production system has at least 2 production units, each producing at least 100 % of the water needed, or 3 units, each producing at least 50 % of the water needed Each production unit has a conductivity meter activating an alarm in the control room when the salt content of the produced water is too high, and the produced water is automatically dumped As extra safety, there is an extra stage of conductivity measuring and dumping before the water is conducted to the potable water tanks For evaporators: The heating medium does not contain any harmful components that may pollute the potable water system if a leakage occurs. All additives are approved

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7. Alkalizing filter Alkalizing filter is placed ahead of the potable water tanks, preferably connected to the recirculation pipe It is possible to add CO 2-gas to the water ahead of the filter There is sufficient water pressure to enable back flushing of the filter with potable water The filter is easy to fill, empty and clean internally

8. Bunk ering station There are at least two bunkering stations, placed on either side of the unit The bunkering hoses are protected with a cap/plug The bunkering hoses can be flushed without any flush water entering the potable water tanks The flush water pipes and valves have the same (or larger) dimension and capacity as the feeding pipes to the storage tanks The flush pipe is constructed to prevent flush water from causing inconvenience to the bunkering station attendants, the supply vessel crew and other personnel Each bunkering station has a test tap placed up-stream the shut-off valve The bunkering pipes have a low point drain to facilitate complete draining of the pipes after bunkering The bunkering station is clearly marked ”Drikkevann / Potable water” in blue colour

9. Chlorine dosing unit(s) A chlorine dosing unit is permanently installed and connected to the filling pipes for the storage tanks A chlorine dosing unit is permanently installed and connected to the recirculation pipes for the storage tanks The chlorine dosing unit(s) have sufficient capacity to disinfect all water at maximum supply speed The chlorine dosing is regulated by a flow meter The water from the bunkering station can not be fed to the storage tanks without passing the chlorine dosing unit The chlorine dosing unit is placed as close as possible to the dosing point, minimizing the length of the hose between the chlorine dosing unit and the bunkering/recirculation pipe The chlorine dosing unit is clearly marked and is safeguarded against pollution The chlorine dosing unit, including the flow meter regulation, has been verified to function

10.

Storage tanks for potabl e water

The potable water tanks are designed to make cleaning and maintenance easy: without inside frames, horizontal stiffeners etc, and with sufficient height to enable work to be done without scaffolding or working in uncomfortable positions The unit has a sufficient number of storage tanks with adequate storage capacity, ref. table below. The table shows minimum total storage capacity for the different types of potable water systems. The values given state total number of days all the tanks combined can supply water when the unit is fully manned. The tanks must be approximately the same size: Recommended total storage capacity for:

Number of storage tanks 2 3 or more Unit based on bunkering only Not recommended! 20 days capacity Unit with one production unit with 100 % capacity, plus 20 days capacity 15 days capacity bunkering Unit with two production units with 50 % capacity each, 15 days capacity 10 days capacity plus bunkering Unit with three units with 50 % capacity or two units 8 days capacity 5 days capacity with 100 % capacity each, plus bunkering

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The tank inlet and outlet are placed far away form each other to facilitate circulation of all water in the tank during bunkering and normal operation, this to enhance mixing of chlorine and to prevent pockets of stagnant water. Bunkered and re-circulated is pumped into the tank in an angle that enhances circulation of the full water volume in the tank, and return inlet, if any, from the distribution network is located as far apart from the tank outlet as possible Automatic valves or other physical measures ensure that water can not be bunkered or re-circulated into a tank that at the same time is supplying the distribution network, and that return inlet from distribution network, if any, is routed into the same tank this water was supplied from The tanks are placed well protected against heat from the surroundings. Water temperatures above 20 o C should be avoided The storage tanks are equipped with test taps to enable water tests to be taken directly from the tanks without feeding the water through to the distribution system The tanks have a circulation system feeding the water from one tank via a chlorine dosing unit and back to the same tank, without going through the distribution system. The pump and piping that is used for this recirculation have sufficient capacity to circulate the tank quickly. The distribution system can simultaneously be supplied from another storage tank The tanks are accessible for necessary maintenance during operation The tanks are equipped with sufficient ventilation The ventilation system is protected against pollution and the openings are covered with a fine net of corrosion proof material The potable water tanks can be completely drained The potable water tanks are equipped with an automatic level meter connected to a manned control room The potable water tanks have no joint walls with other tanks carrying petroleum products, liquid chemicals etc The tank roof should not be part of a deck in a ”dirty area” Pipes carrying other products than potable water are not carried through the potable water tanks. If this has not been possible, these pipes are carried through in open ducts Internal coating products used for potable water tanks have been approved by the NIPH It is documented that the coating has been applied according to vendor’s specifications with regard to method of application, thickness, washing and hardening of such coating. After filling the tank, smell, taste and hydrocarbon content of the water has been verified 11.

UV-units

UV-units are approved by the NIPH, and will be used according to type approval specifications The UV-units are biodosimetrically tested and give an UV-dose of 40 mWs/cm 2 (for newbuilds and when upgrading old units, approved UV-units that only give a dose of 30 mWs/cm 2 are no longer recommended) The UV-units have been dimensioned to handle the poorest water quality that meets the potable water regulations (with a colour number of 20, Norwegian water typically has an UV-transmission somewhat below 30 %/5 cm, and offshore units must be able to handle bunkered water) At least two UV-units have been installed. With just two units, each must be capable of disinfecting all potable water at maximum supply rate (peak values). With three units installed, each of these must be able to disinfect 50 % of the water When two or more UV-units are used in parallel, it must be ensured that the water is evenly distributed between the units The UV-treatment is the final stage in the potable water treatment system prior to distribution Each UV-unit has a sensor, measuring radiation intensity. If the intensity falls below accepted levels, or if the power fails, the water supply is automatically shut down Each UV-unit has a timer and an alarm lamps for each UV-radiation chamber There is a cartridge filter connected up-stream of each UV-unit (maximum pore size 50 micrometers) Test sampling of the water is made possible just before and after the UV-unit 62


12.

Water dist ribu tion sys tem

Pipe material, pipe type and quality are chosen to withstand exposure to water of varied quality. The same applies to fittings Potable water pipes outside living quarter areas are marked ”Drikkevann” and/or ”Potable water” in blue colour Potable water pipes are not carried through tanks carrying other products than potable water. If this is not possible, those pipes are carried through in open ducts. External pipes are protected against frost and heat Pipes with stagnant water have been avoided In case of contamination it is possible to drain the entire potable water system Connections to other liquid carrying systems are sufficiently safeguarded and broken/atmospheric connections chosen where this has been feasible. All other connections are safeguarded by verifiable technical barriers, see 9.2.5 Normal hoses connected to the potable water system are equipped with at least one verifiable nonreturn valve Hot water tanks deliver enough hot water to maintain at temperature of at least 60° C at the coldest point in the system (measured after flushing the water for one minute)

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Append ix 2 – Check list for oper ational doc umentation of a pot abl e water syst em (Potable water m anual) The requirements are described in chapter 3. The operational documentation can be organized in various manners. Traditionally, offshore units have had voluminous potable water manuals, but it has become more common to integrate the main part of the documentation in the general operational system for the unit. By this integration, the manual simply becomes a key document, describing how the actual operational documentation is organized. This check list is based on the normal content of traditional potable water manuals, but may also be used to check if it is easy to find similar documentation when these documents are integrated in the general operational system: General information: 1. Does the manual contain a table of contents (where/page no.)? _______________________________ 2. Does the manual have a distribution list (where/page no.)? __________________________________ 3. Is revision date for the manual stated (where/page no)? _____________________________________ 4. Does the manual have a general description of the entire potable water system (where/page no.)? ___________________________________________________________________ 5. Does the manual have a schematic drawing of the entire potable water system (where/page no.)? ___________________________________________________________________ 6. Does the manual state persons responsible for the various parts of the potable water operational system (platform manager, medical and technical personnel, onshore organization etc.) (where/page no.)? ___________________________________________________________________ 7. Does the manual have a reference list to all documents referred to (journals, drawings, procedures, maintenance system, manuals, regulations etc. (where/page no)? ______________________________ 8. Does the manual describe the potable water education programmes needed for the medical and technical personnel before being assigned their specific tasks within the potable water system, see 3.2 (where/page no.)? ___________________________________________________________________ 9. Does the manual describe how this level of knowledge is maintained, see 3.2 (where/page no.)? _____ 10. Does the manual describe the documentation medical and technical personnel have to be familiar with before taking responsibilities for their specific tasks, see 3.2 (where/page no.)? __________________ 11. Are maintenance requirements of the system described, see 3.3 (where/page no.)? _______________ 12. Is it stated that all chemicals that directly or indirectly (through leakages, when cleaning etc.) may come into contact with potable water must be approved, see 2.3.4 (where/page no.)? ______________ 13. Are routines for handling non-conformities according to chapter 3.5(where/page no.)? ___________ 14. Are routines for applying for excemptions according to chapter 3.8 (where/page no.)? ____________ 15. Are potable water problems included in the emergency preparedness plans for the unit, see 3.6 (where/page no.)? _________________________________________________________________ 16. Does the company have routines for internal audits to verify that technical systems and management systems are functioning and are revised when necessary, see 3.7 (where/page no.)? _____________ 17. Are there routines safeguarding that the authorities are always informed of any significant system changes, that may be made in the future (where/page no.)? __________________________________ Sea water system: 18. Is there a general drawing of the sea water system (where/page no.)? _________________________ 19. Is there a general drawing showing vertical and horizontal distance between the sea water inlets and the various discharge points (where/page no.)? __________________________________________ 20. Is it explicitly emphasized that water production has to stop if the sea water is contaminated (where/page no.)? __________________________________________________________________ 21. Are equipment and chemicals to be used in sea water production described (where/page no.)? __________________________________________________________________

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22. Can it be guaranteed that methods of anti-fouling that are being used for the sea water system will not pollute the potable water (where/page no.)? __________________________________________ Water production units: 23. Is operating routines for the water production units described and illustrated on drawings (where/page no.)? __________________________________________________________________ 24. Is the use of chemicals in the water production described, (including cleaning chemicals): type of chemicals, product names, producers, maximum doses and dosing adjustments etc. (where/page no.)? __________________________________________________________________ 25. Is the measuring of conductivity of produced water described, and procedures described in case the conductivity is too high and sets off the alarm (where/page no.)? _____________________________ 26. Is the alarm limit for the conductivity meter listed (maximum 6mS/m for evaporation and 75 mS/m for reverse osmosis) (where/page no.)? __________________________________________________ Bunkering potable water: 27. Are the bunkering procedures according to recommendations in appendix 10 (where/page no.)? ___________________________________________________________________ 28. Is the logging procedure for bunkering according to recommendations stated in appendix 5 (where/page no.)? __________________________________________________________________ Alkalizing unit: 29. Are the procedures for alkalizing documented and drawings of the system enclosed (where/page no.)? ___________________________________________________________________ 30. Is the filter material described (where/page no.)?___________________________________________ 31. Is the procedure for back-flushing of the filter described (where/page no.)? _____________________ 32. Is the procedure for change of filter material described (where/page no.)? ______________________ 33. Are the procedures for pH-control described (where/page no.)? _______________________________ Chlorination unit: 34. Is type of chlorine, concentration and dosing described (where/page no)? _______________________ 35. If sodium hypochlorite is used: Are routines established to ensure that the chlorine will be exchanged before expiring date (where/page no.)? __________________________________________________ 36. Is it made clear that the free chlorine level shall be between 0.1 and 0.5 mg/l Cl 2 half an hour after chlorination (where/page no.)? ________________________________________________________ UV-unit: 37. Is the maximum disinfection capacity of the UV-units at the poorest water quality (UV-transmission somewhat below 30 %/5 cm) stated (where/page no.)? _____________________________________ 38. Is the maximum lifetime for the UV-radiation tubess stated (where/page no.)? ___________________ 39. Are routines for calibration of the UV-sensors described (where/page no.)? _____________________ 40. Is the clearly described how the UV-unit, including quarts glass, UV-sensors etc, is to be cleaned if radiation intensity falls (where/page no.)? ________________________________________________ 41. Is it stated at what intensity level the automatic shut-off valve is activated (where/page no.)? _______ Potable water tanks: 42. Are operation routines for storage tanks described (where/page no.)? __________________________ 43. Are procedures for cleaning and disinfection of the storage tanks in accordance with recommendations made by the NIPH, see appendix 13 (where/page no)? _______________________ 44. Will the specific protective coating, that may be used on patches or re-coating of the tanks, harden sufficiently under the existing temperatures (both air- and tank material temperatures) (where/page no.)? __________________________________________________________________

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45. Have procedures been established for documenting that requirements for method of application, coating thickness, washing and hardening have been followed when coating have been applied in potable water tanks (where/page no.)? __________________________________________________ Potable water distribution system: 46. Are the procedures for cleaning and disinfection of the distribution system in accordance with recommendations made by the NIPH, see appendix 12 (where/page no.)? ______________________ 47. Are operation and maintenance routines for pressure tanks described (where/page no.)? ___________ 48. Is it emphasized that all hose couplings should be disconnected after use (where/page no.)? ________ 49. Is it emphasized that connections to the potable water system must not take place if back-suction/ back-flow can lead to contamination of the potable water (where/page no.)? ____________________ 50. Is it stated that the thermostat of the water heater must be set to ensure that the water on the coldest o place in the distribution network holds at least 60 C after one minute of flushing (where/page no.)? __________________________________________________________________________________ Measuring, logging and reporting of water quality: 51. Is the daily logging procedure in accordance with the recommendations given by the NIPH, see appendix 3 (where/page no)? _________________________________________________________ 52. Are the monthly and yearly potable water analyses in accordance with recommendations given by the NIPH, see appendix 4 (where/page no)? _________________________________________________ 53. Is the water sample programme varied, with several samples each month and differention through the year, giving a good picture of the water quality throughout the system (where/page no)? ___________ 54. Are procedures for physical/chemical and bacteriological water tests in accordance with recommendations given by the NIPH, see appendices 7 and 8 (where/page no)? ____________________________ 55. Is the use of measuring devices described (where/page no)? _________________________________ 56. Is a daily, separate log kept for the technical equipment of the water production system (where/page no.)? ___________________________________________________________________ 57. Are routines established for tracking malfunctions in the potable water system (where/page no.)? ___________________________________________________________________ 58. Are routines established for a half-yearly or yearly internal report on the potable water quality, with a copy to the NIPH, see 3.8 (where/page no.) ___________________________________________

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Append ix 3 – Example of a daily potable water logb ook Month: ______________________ Date

Smell

Taste

Appearance

pH

Free chlorine mg/l

Total chlorine mg/l

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

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Conduc- Remarks tivity mS/m

Signature


Ap pend ix 4 – Recommended analysis programme and qu ality requirements Parameter Smell

Frequency* Unit D/B/M Subjective evaluation Threshold value

Remarks Cf. with taste samples ”

Taste

D/B/M

Subjective evaluation Threshold value

Cf. with smell samples ”

Appearance

D/B

Subjective evaluation

pH-value

D/B/M

Conductivity

D/B/M

The water shall not be corrosive MilliSiemens/m Note: Alarm for the o (mS/m) at 25 C production unit is set at: (1 mS/m = 10 μS/cm) - 6 mS/m for evaporator - 75 mS/m for reverse osmosis unit, see 4.3.1

Free chlorine

D

Milligram/l

B

Daily chlorine analysis not necessary on for systems only using UV-disinfection. Measured 30 minutes after ended bunkering. Chlorine analysis not necessary on a daily basis for systems using UV-disinfection Note: Has to be low in produced water

Limit values Not obvious 2 at 12o C 3 at 25o C Not obvious 2 at 12o C 3 at 25o C Clear and without discolouring 6.5-9.5

Normally 10. Higher value acceptable for reverse osmosis produced water, as well as for bunkered water, when the same high level is documented at the delivering onshore water works, see 4.3.2 0.1-0.5, see 4.3.1

See above.

Total chlorine

D

Milligram/l

1.0, see 4.3.1

Colour

B/M

Milligram Pt/l

Turbidity Clostridium perfringens E. coli

M M

FNU Number/100 ml

M

Number/100ml

Intestinal enterococci

M

Number/100ml

Calcium

M

Milligram Ca/l

Colony count at 22o C/ 72T Coliform bacteria Iron Copper

M

Number/ml

M

Number/100ml

0

M M

Milligram Fe/l Milligram Cu/l

0.2 0.3 in cold water, see 4.3.3

20 1 0

Findings to be reported immediately to supervisory control authorities Findings to be reported immediately to supervisory control authorities No analysis needed unless the water is alkalized Shall be below 10 after the disinfection unit

68

0

0

Recommended values: between 15 and 25 100


Table cont’d Parameter 1.2-dichlorethane Ammonium Benzene Benzo(a)pyrene Lead Bromate Cadmium Chemical oxygen use, COD-Mn (KMnO4)

Frequency* A A A A A A A A

Unit Microgram/l Milligram N/l Microgram C 6H6/l Microgram/l Microgram Pb /l Microgram BrO3 /l Microgram Cd/l Milligram O/l

Remarks

Hydrocarbons, mineral oils

A

Microgram/l

10

Polycyclic aromatic hydrocarbones (PAH) Tetrachlorethane and trichlorethane Trihalomethanes UV-transmission

A

Microgram/l

0.10

A

Microgram/l

10

A A

Microgram/l Percentage

50 See chapter 4.3.4.

Glycols

A

Microgram/l

TOC may alternatively be measured

Analysis necessary only when using UVradiation of water Analysis necessary only when glycols are added to systems that may pollute the potable water if leakages occur.

Limit values 3.0 0.50 1.0 0.010 10 5 5.0 5.0

10

* Frequency is divided into daily analyses (D), analyses when bunkering (B), monthly analyses (M) and annual analyses (A)

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Ap pend ix 5 – Bunkering log Bunkering date: _________________ Supply vessel:

Time when bunkering was finished: _________________

______________________________________________________________________

Does the supply vessel chlorinate the water (Y*/N)?

____________________________________

Delivering water works onshore: _________________________________________________________ Normal conductivity at the onshore water works (mS/m): ______________________________________ Water amount to be bunkered: _______________

Amount of chlorine added: ___________________

Water sample results from each tank the supply vessel delivers water from: Tank no.: Colour: Smell: Taste: Appearance: Conductivity (mS/m): pH-value: Is the water acceptable (Y/N)?

1

2

3

Quality parameters: 20 mg/l Pt Not obvious Not obvious Clear** 10 mS/m, or equal to delivering water works*** 6.5 – 9.5

Water sample results from each tank the water is being bunkered to. Samples shall be taken at least 30 minutes after completed bunkering: Tank no.: Chlorine measuring time Free chlorine (mg/l) Total chlorine quantity (mg/l) Is the water acceptable (Y/N)?

1

2

3

Quality parameters:

0.1 – 0.5 mg/l Normally below 1.0 mg/l, see 4.3.1

Signature by person responsible for the bunkering: _______________________________________

* In general supply vessels do not need to chlorinate the water, as disinfection is ensured through the use of both chlorine and UV-light on the offshore unit. Further chlorination increases the risk of exceeding the limit value for trihalomethanes, and should only be done if the supply vessel can document good chlorination systems and routines. But as this is in one extra step of chlorination, the offshore unit should increase the monitoring frequence for chlorination by-products. ** Strong light and white background is best to detect dark particles, black background for light particles. ***Higher values than 10 mS/m (equals 100 μS/cm, see 4.6) can be accepted, if it is documented that such values are normal at the onshore water works where the supply vessel bunkers the water. Several Norwegian water works have introduced water treatment that is increasing the conductivity level to be between 10 and 15 mS/m. 70


Ap pend ix 6 – Recomm ended r equir emen ts t o s upp ly b ase and vessels The water quality shall be maintained during transport. Both the supply base and the supply vessel must be able to document satisfactory routines for control and handling of the potable water. Below is a list of potential requirements to be met when signing a contract for delivery of potable water. The list is meant as an example on procedures ensuring a safe and well documented potable water quality. Requirements to supply bases: 1. Only use supply bases receiving potable water from approved water works with good quality water. 2. The supply base shall be able to document the normal water quality from the supplying water works. The water works is required to have updated information on the potable water quality available to the recipient of the water. An annual report on the water quality should be available, and it is especially important to list the intervals within which the conductivity will vary, see item 9. Such normal conductivity values should be reported to the supply vessel crew. 3. The supply base should have an agreement with the water works on the maximum pump speed applied when pumping to the supply vessel, and make sure that this pump speed is not exceeded. A pump speed that is too high can result in back-suction of contaminated water from the pipe system. 4. If the supply base is storing potable water on tanks from which water is bunkered, these tanks have to be cleaned and disinfected frequently since they often and regularly are refilled, thereby causing new deposits to form, see procedures in appendix 13. 5. The bunkering station must have a suitable design. 6. Before bunkering is taking place, bunkering hoses and pipes must be flushed a few minutes with the same pump speed as when filling the supply vessel tanks. 7. The supply base must have a quality system ensuring safe operation and maintenance, including water sampling for analyses. Supply vessel requirements: 8. Dump remaining water in tank before bunkering from shore. 9. After hoses and pipes on the supply base have been flushed, the supply vessel crew shall take samples to document the quality of the received water before bunkering starts. The tests should include colour, smell, taste, appearance and conductivity. The water shall be accepted only if the requirements stated in chapter 4.3.2 are fully met, and when conductivity is within the limits stated by the water works, see item 2. The results shall be logged, and may later be used as documentation in case the water is contaminated after the supply vessel received the water from the supply base. 10. Due to increased risk for formation of disinfection by-products, the supply vessel normally should not chlorinate (or ozonate) the water. Chlorination may only be done under strictly controlled conditions. 11. The storage tanks shall be cleaned and disinfected at least every 3 months, see appendix 13. Water tests will show if this frequency is sufficient. 12. The supply vessel crew should regularly test the water quality in the storage tanks, see appendix 4. Tests should be done just before and just after cleaning, see item 11, and under normal operation. This will also confirm that the cleaning frequency is adequate, see also annual procedure in item 15. 13. Protective coating in the storage tanks should be certified, see 2.3.4. To document that a new protective coating has been sufficiently hardened, water samples should be analysed for hydrocarbons (before and after coating application) and for presence of the most volatile coating components. 14. The supply vessel must have a quality system that ensures safe operation and maintenance. Annual quality test of the entire supply chain: 15. The offshore unit should once a year test if and how the potable water quality varies throughout the supply chain. This is achieved by a test sampling from the supply base, the storage tanks on the supply vessel, the bunkering station and finally from the storage tanks after the water has been chlorinated. These samples should be analysed at an accredited laboratory, and should include parameters suggested in 4.3.3. A comparison of how the quality of the same water varies all through the supply chain will indicate improvement possibilities.

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Appen dix 7 – Instructions for bac teriolog ical testing of potable water Sample bottles The laboratory gives instructions on what type of sample bottles to use and how to handle the bottles. Sampling from tap 1. Remove any strainers from the tap. 2. The spout of the tap is sterilized with a spirit flame (a match will do if necessary). If the use of an open flame is not allowed, the sample point can be disinfected in the following manner: make sure the tap spout is emptied of water. Fill a water glass with 70 % alcohol or a concentrated chlorine solution. Submerge the tap spout into the solution for 30 seconds. 3. Let the water flush for at least 3 minute before the sample is drawn. 4. Remove the cap carefully from the sample bottle without touching the rim of the bottle opening. 5. Fill the bottle with water. 6. Close the sample bottle carefully without touching the cap or the bottle opening. 7. After the test sampling, measure the water temperature at the sample point. Packing and shipment 1. The bottles should be clearly marked with sender, sample point, date, time, and water temperature. The marking should be water proof. 2. The bottles are to be sent as soon as possible in a clean container (for instance a thermo box). The samples should preferably reach the laboratory within 4 hours after sampling. If the transportation time exceeds this, the samples have to be chilled to between 2 and 10 o C during transportation and put o in a refrigerator (about 4 C) upon arrival at the laboratory if the analysis cannot take place immediately. The time between sampling and analyzing shall not exceed 30 hours. 3. Test samples are to be sent as soon as possible to the relevant laboratory. 4. Test samples that are not packed and sent according to directions can not be analysed. 5. An analysis arrangement should be made with the laboratory before samples are sent.

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Append ix 8 – Instruc tions for phy sio-chem ical sampl ing , inc ludi ng annu al analyses Monthly physio-chemical sampling The laboratory gives instructions on type of sample bottles to use and how to handle the bottles. Annual physio-chemical potable water analysis Several annual analyses require use of special bottles. Special bottles should be requisitioned from the laboratory performing the analyses. A random test tap in the distribution system is chosen at a random time, day or night. The water is flushed from the test tap to get rid of stagnant water from the fittings. Fill the bottles with cold water. First the bottles for heavy metal analyses should be filled, thereafter special bottles for the different organic parameters, and finally a one litre bottle is filled, all from the same sample point.

If the values for the heavy metals lead or cadmium are exceeded, it is necessary to take an extended sample from the very same sample point: Extended heavy metal sample Special bottles for heavy metal analyses are requisitioned from the laboratory doing the analyses. These bottles shall not be cleaned before use. 1. The sample point must not have been in use for the past 10 hours before the sampling takes place. 2. A sample is taken of the first cold water being tapped. 3. Following a one minute continuous flushing with the tap fully opened, a new sample is taken. 4. The water samples should be analysed for lead, cadmium, chrome, mercury and nickel.

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Ap pend ix 9 – Tr oubl eshoo ti ng g uid e PROBLEM A. Bad smell/taste

POSSIBLE CAUSE 1. Contaminated water from the supply vessel 2. Water containing sodium from the production unit 3. Newly painted storage tanks (including those on the supply vessel). Chemical substances in the coating may have reacted with chlorine

4. Organisms contaminating sea water inlet (e.g. algae)

B. High colour values (yellow/ brown water) C. Turbidity (particles)

D. Low pH

5. Oil polluting the sea water inlet 6. Microbial growth in storage tanks and/or distribution system 7. High iron content 8. High copper content 9. The water may have been exposed to UV-radiation too long 10. Overdose of chlorine (sodium- or calcium hypochlorite) 1. Water from the supply vessel contains humic particles 2. High iron content 1. High iron content (iron corrosion clusters) 2. Stormy weather conditions may have stirred up particles from the bottom of the storage tanks 3. After switching tanks, particles may have been sucked up from the tank bottom 4. Particles in the water from the supply vessel 1. Water delivered from the supply vessel with low pH value 2. The by-pass valve on the alkalization filter is “too open”

3. The alkalizing filter contains an insufficient amount of filter mass

4. The filter mass is ineffective 5. If calcium-/CO2-unit being used: a. CO2-dosing is too high b. Not enough filter mass in the alkalizing filter 6. Error in measuring pH-level

CORRECTIVE MEASURES Water with bad smell/taste shall not be accepted for bunkering See problem G, item 3

Check that the supplier’s instructions regarding hardening temperature, time and humidity have been followed, see 9.1.4. Try reducing the chlorine dose without reducing the microbiological qualities. Active carbon filter may remove some smell- and taste components Change sea water inlet or stop the fresh water production. Active carbon filter may remove some smell and taste components Same as item 4 See problem J See problem L See problem L Reduce number of UV-units in operation, or establish continuous water flow Reduce chlorine dose, but make sure that the concentration is within the required levels of 0.1–0.5 mg Cl 2/1 Water containing humic particles shall not be accepted for bunkering See problem L See problem L. In addition cleaning or renewal of pipes may be necessary More frequent cleaning of the potable water tanks

More frequent cleaning of the storage tanks is necessary

Water containing particles shall not be accepted Water with a pH lower than 6.5 shall not be accepted unless the water can be alkalized before distribution Adjust the by-pass valve to increase amount of water flowing through the filter. This should be followed up with a new pH control sampled after the alkalization filter Refill and back flush the filter. Check the pH level after the alkalizing filter. When about 30 % of the filter mass has been used, or when pH level higher than 7.5 is not obtainable even if the by-pass valve is closed, new filter mass should be added Replace the entire filter mass Use smaller dose of CO 2 See item 3 See problem F

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PROBLEM E. pH value exceeding requirements

POSSIBLE CAUSE 1. The water from the supply vessel exceeded the required pH level

2. The by-pass valve on the alkalization filter is not adequately opened

3. If lime-/CO 2-unit is used: a. CO2-dosing is too low b. Recent refill of filter mass in the alkalizing filter 4. Error in measuring pH level F. Error in pH- 1. Old buffer solution measuring (deviation of more than one pH-unit between offshore and onshore tests) 2. Water produced by evaporation/reverse osmosis has low buffer capacity 3. Old electrode 4. pH-electrode is ”dry” or there is air inside the glass membrane 5. Gel filled pH-electrode 6. Old battery 7. Error in the instrument 1. Water from the supply vessel is G. High conductivity (= polluted by sea water high salinity 2. Salt water in the bunkering hoses 3. Salt water from production unit for potable water because of: a. Error in the conductivity meter on the production unit or in the laboratory

H. Insufficient UV-disinfection

CORRECTIVE MEASURES The water may not be accepted if pH level is above 9.5. (may be caused by cement lined storage tanks on the supply vessel) Adjust the by-pass valve to decrease the amount of water flowing through the filter. This should be followed up with a new pH control taken after the alkalizing filter. High pH is normal after replacing filter mass

Use a higher dose of CO2 See item 2 See problem F Replace buffer solution and calibrate the pH- gauge. Buffer solutions must be stored capped. Recommended pH-value for the buffer solution being used when calibrating is pH=7.0 and pH=9.0. The buffer solution shall be clear and without sediment or algae growth Employ water treatment that increases the alkalinity Note! Water with low buffer capacity is very sensitive to variations in pH level Replace electrode Add new electrolyte/remove all gas bubbles. The electrode may have to be replaced The electrode shall have a liquid inner electrolyte Replace battery and re-calibrate Have the instrument repaired/replaced o With a conductivity above 10 mS/m (100 μS/cm) at 25 C the water should be refused if it can not be confirmed that it is a normal conductivity for that particular water Bunkering hoses shall be flushed before sampling

See problem F, item 6 and 7. Error in the conductivity meter is discovered when there is a difference in conductivity measured offshore and onshore Repair the leakage Replace membrane

b. Leakage in the evaporator condenser c. Damage to the reverse osmosis membrane d. Sedimentation in the reverse osmosis/- Clean the production unit regularly evaporator unit 1. ”Dirty” radiation tubes in the UV-unit Clean the radiation tubes 2. Malfunction in the UV-tubes, or the maximum operation time allowed has been exceeded 3. Particles in the water or discoloured water 4. High temperature on the UV-tubes 5. Malfunction in the magnetic valve 6. The UV-unit is not working properly

Change UV-tubes. The time recorder should be checked regularly. Radiation tubes shall be replaced at the maximum operation time or earlier if necessary See problem B and C, item 1. Note! Muddy/discoloured water (high turbidity/high colour count) may trigger the automatic closing of the valve See maintenance instructions Shut down the UV-unit until the valve has been repaired or replaced Check the effect by testing the colony count before and after the UV-unit

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PROBLEM I. Insufficient chlorination

POSSIBLE CAUSE 1. Operation procedures have not been followed 2. The chlorine solution is too old. Sodium hypochlorite lasts around 3 months. Calcium hypochlorite lasts nearly indefinitely as granulate or powder 3. The chlorination equipment is defect 4. The water requires more chlorine, compare with values for total chlorine 1. Contaminated water from the supply vessel

CORRECTIVE MEASURES Enforce the operation routines

If sodium hypochlorite is used – replace the solution. If calcium hypochlorite is used – make a new solution

Check the equipment for defects Higher chlorination dose may be necessary

Make sure that the disinfection unit is working, see problem H or I. Check bunkering routines. Possible causes may be contaminated bunkering hoses, low flush water pipe capacity or failure in supply vessel routines 2. Microbial growth in the water because Make sure that the disinfection unit is working, see of a high content of organic substances problem H or I. If it is working properly, it is important or prolonged presence in the potable to locate where in the distribution system the problem is water system. This may result in originating. This is done by testing the water quality in microbial growth on tank walls and the the tank, before and after the different treatment units distribution system and from some taps in the distribution network. A thorough cleaning and disinfection of the tanks and/or the distribution system may be necessary. The filters in the distribution system are especially susceptible to such growth, and the filter mass should be replaced 3. The potable water is contaminated Make sure that the disinfection unit is working correctly. through air vents or couplings, or in See problem H or I. Secure possible contamination connection with maintenance work sources and assess procedures Make sure that the disinfection unit is working correctly. K. E.coli, Clos- 1. Contaminated water from the supply tridium perfrin- vessel See problem H or I. Check bunkering routines. Possible cause may be contaminated bunkering hoses, inferior gens, intestinal flush water pipe capacity or failure in the supply vessel enterococci or routine coliform bacteria 2. Contaminated sea water to the potable Make sure that the disinfection unit is working correctly. water production See problem H or I. Make sure that the best suitable sea water inlet is being used 3. The potable water is contaminated Make sure that the disinfection unit is working correctly. through air vents or couplings, or in See problem H or I. Secure possible contamination connection with maintenance work sources and assess procedures pH must be adjusted to be between 7.5 and 8.5. See L. High content 1. Low pH problem D of iron or copper 2. Low alkalinity Use water treatment that increases alkalinity (corrosion) 3. High sodium content See problem G J. High colony count

M. High content of heavy metals such as lead/cadmium N. Trihalomethanes

4. Stagnant water in copper pipes 5. Tapping water from hot water taps 1. Corrosion

Flush the water before using it for drinking/cooking Use cold water only for drinking and cooking See problem L

1. These substances may develop when electro chlorinating sea water inlets and since they are volatile may increase in concentration over evaporators 2. Limit value offshore may be exceeded if water bunkered from onshore water works contain much trihalomethanes

Reduce chlorination in the sea water inlets or install active carbon filter

Adjust the chlorination on the offshore unit, change to supply from another water works or install active carbon filter

76

Sufficient, Safe and Good Potable Water Offshore PROBLEM

O. Bromate

POSSIBLE CAUSE

CORRECTIVE MEASURES

If electro chlorination is used prior to Reduce electro chlorination, reduce the effect of the evaporation, the bromate level in the evaporators, thus producing cleaner water, or potable water may be exceeded. The installing active carbon filter level will depend on pH, and may increase after UV-treatment

77


Append ix 10 – Recommended procedu res for bun kering potable water The procedures should be adjusted to the system on the specific unit. Before bunkering: 1. If possible: Dump remaining water in the tank to be bunkered to. 2. Check that a sufficient amount of hypochlorite with the correct concentration is prepared. The solution must not be too old. The hypochlorite amount should be adjusted according to experience made during previous bunkering. If the pump is not operated by a flow meter, the dosing speed must be calculated. 3. Check that the valves on the chlorine dosing system are opened. Start the pump to ensure that it is operating properly. 4. Check that water is not distributed from the tank being bunkered to. 5. Check that the shut-off valve on the bunkering station is closed. 6. Check that the flush valve is open. 7. Check number of tanks the supply vessel is going to deliver water from. During bunkering: 8. The bunkering hoses are connected to the supply vessel and flushed by way of the drain valve. 9. After the flushing is completed, a water sample is taken. If water is bunkered from more than one tank on the supply vessel, a water sample shall be taken from each one of the supplying tanks. Colour should be measured and smell, taste and appearance should be logged. Water that does not meet the requirements should be rejected as potable water. Conductivity is measured and should not deviate from the values logged from previous bunkerings. This is to ensure that the conductivity measured on the bunkering station is approximately the same as conductivity measured on the supplying water works onshore, and normal values onshore should be obtained from this water works. To avoid long discussions with the supply vessel captain, it is advisable to get a second opinion before rejecting water due to smell, taste and appearance. 10. If the water is accepted, the bunkering can start. The drain valve is closed, the chlorine dosing pump started, and the water is pumped to the storage tanks onboard the offshore unit. 11. The chlorine dosing pump is stopped when the necessary calculated amount of chlorine has been added. After bunkering 12. The storage tank is kept isolated for 30 minutes. 13. Analyse a water sample from the storage tank for free residual chlorine. The content should be within 0.1-0.5 mg/l. When too little chlorine has been added during bunkering, the water must either be dumped or additional chlorine added to the water by recirculating the tank content through the chlorination unit back to the tank to achieve a sufficient mix of new chlorine in the water. Items 12 and 13 are repeated. 14. Measured results should be logged, see appendix 5.The dosing pump should be adjusted to the same level at the next bunkering.

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Append ix 11 – Calcul ation s in connect ion with chl orinat ion Stored chlorine in dissolved form loses its strength after a while. Content of the various substances in different types of potable water require different chlorine doses to achieve sufficient free residual chlorine after the 30 minutes of contact time. The following calculations must be seen as examples only, and must be adjusted to the particular type of water being treated. When experience builds up regarding dosage, bunkering time and so forth, calculations may not be necessary, as the bunkering log, see appendix 5, will give the necessary information on chlorine volume, necessary pump speed, mixing ratio, etc. 1. What is the required chlorine level? Regardless of method used, such as Flowmeter regulated chlorination or manually regulated pump, the chlorine amount must be calculated. When calculating the correct grams of chlorine to be used, it is important to remember that calcium hypochlorite holds 65 % free chlorine, while sodium hypochlorite holds only 15 % free chlorine, see 8.2.2 and 8.2.3.

If the storage tank being bunkered to already contains substantial amounts of water, extra chlorine must be added to obtain the correct chlorine solution. If the water quality does not fluctuate, this means that it is always the same amount of chlorine that is required when filling a tank. The chlorine solution strength and/or the pump speed may vary. It is preferable to avoid bunkering to storage tanks already containing substantial amounts of water, since this may make it difficult to blend in the chlorine properly. 2. How to make a chlorine solution of a specific concentration? The amount of disinfectant needed to make 1 litre of solution of a specific concentration is as follows: For sodium hypochlorite: Wanted concentration (%) x 1000 ml Chlorine % in the chlorine container - The answer gives ml solution to be mixed with the water, and the amount of water plus the amount of solution together is one litre.

For calcium hypochlorite: Wanted strength (%) x 1000 g Chlorine % as powder or pills - The answer will give number of grams to be dissolved in one litre of water. 3. Calculation example for a flow regulated pump Let us say we have a potable water tank holding 130 m 3. The tank is almost empty. We are going to fill it up completely, and experience from previous bunkering shows that we need 1.0 gram chlorine per m 3.

Necessary chlorine amount: Total need is 130 m 3 x 1.0 g/m3 = 130 grams of chlorine to disinfect the entire amount of water in this tank Bunkering time: 3 Dosing speed for chlorine the pump is 20 litres per hour, and 200 m per hour is going to be bunkered

(If we, for instance, already had 30 m 3 water in the tank when the bunkering started, the bunkering time 3 for the remaining 100 m would have been 0.5 hour). 79


Necessary chlorine concentration in the solution: Number of grams (g) chlorine to be added to the entire bunkering volume Bunkering speed (l/hour) x bunkering time (hour)

10 g/l equals 1 % chlorine solution. If the tank is emptied before bunkering, the required amount of chlorine concentration is not necessary to calculate every time, provided that the quality of the water being bunkered is fairly stable. Had the tank already contained 30 m3 of water when the bunkering started, 3 the bunkering time would have been 0.5 hour for the remaining 100 m , and we would have had to increase the chlorine concentration in the solution to 1.3 % to obtain a sufficient disinfection of the entire water content. The calculation example is for mixing 13 litres of 1 % sodium hypochlorite solution. The sodium hypochlorite we have holds 15 % strength, and is approximately 2 months old. It weakens between 1 and 2 % per month, and to be safe we estimate the strength to be 10 %, see 8.2.2:

We need 100 ml 10 % solution to get 1 litre 1 % solution. To make 13 litres of such a solution we need 100 ml x 13 = 1300 ml (= 1.3 litre). The easiest way to make this solution is to add the chlorine to the dosing tank, and then add water to a total volume of 13 litres. Please read the product data sheets and remember to wear protective gear! 4. Calculation example for a manually operated pump 3 3 We are going to bunker 130 m , the tank is almost empty and bunkering speed is 200 m per hour. We need 1 gram chlorine per m 3 and bunkering time is 0.65 hours, see calculations explained above.

Dosing speed calculation: We can use a variety of chlorine solution strength since the chlorine dosing speed can be adjusted. In this example we have a 5 % solution, and here too we need 130 gram of chlorine to disinfect the tank (this chlorine amount would be the same even if we had for example 30 m 3 in the tank to start with). As 3 3 experience has shown, the necessary chlorine dose is 1 g/m , (but it would have increased to 1.3 g/m if the tank already held 30 m 3 of water). The dosing time (litre/hour) for the pump speed is calculated as follows:

The bunkering speed is 200 m 3/hour, and the chlorine solution strength is 5 %, and we want the potable 3 water to hold a chlorine dose of 1 g/m (equals 1 mg chlorine per litre). The result is:

Consequently the chlorine dosing pump should be set at 4 l/hour. Necessary amount of chlorine solution (l) = dosing speed (l/hour) x bunkering time (hour) Necessary amount of chlorine solution = 4 (l/hour) x 0.65 (hour) = 2,6 litres If we had 30 m 3 of water in the tank, the chlorine dosing speed would have to be increased to 5.2 l/hour in order to pump the same 2.6 litres of chlorine solution in half an hour.

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Append ix 12 – Cleani ng and disinfection of a dist ribut ion system Disinfection may be done in different ways, for example by heat treatment (increasing the water temperature of the hot water system to above 70 o C for at least 5 minutes) or by chlorination. Below is a description of a chlorination method where the water may be used as potable water even during the disinfection process. If more concentrated chlorine doses are required, the water is not acceptable as potable water. Using lower doses of chlorine than those described below, is not recommended as this often will not result in satisfactory distribution system disinfection. 1. Preparations: One person is assigned the responsibility for completing the work. Personnel must be informed of the following: - The distribution system shall be cleaned and disinfected with chlorine. - The high chlorine concentration may give the water an unpleasant smell and taste, especially if there is much biofilm in the system. Bottled water should be available for cooking and drinking. - The water may be used for cleaning and personal hygiene (showering), as the values are according to WHO standards for potable water. Coloured clothes washed in this water may become bleached. 2. Adding chlorinated water Fill a potable water tank with water holding a concentration of 5 mg/l free chlorine. Open all taps on the distribution system and let the water run. It should run for a while after the smell of chlorine is obvious. Let the taps drip slowly, thereby allowing new, chlorinated water to be added during the entire disinfection period. To avoid bacterial growth it is important to properly chlorinate places in the distribution system where there may be stagnant water. 3. Measuring chlorine content Measure the free chlorine content on a few water taps, choosing different locations, including the tap farthest away on the distribution system. The free chlorine concentration should be between 4 and 5 mg/l. If the chlorine content is significantly lower in some samples, the water has not been flushed long enough. Following further flushing of all taps in the area, new chlorine samples must be taken. The water may be used during the disinfection. After 12 hours, samples from different locations in the distribution system should be taken (including one sample at farthest location), to document enough remaining free chlorine. 4. The need to repeat the procedure If, after 12 hours, the free chlorine content has decreased more than 1 mg/l in most of the sample spots, repeat the procedure without delay. If unpleasant smell and taste still linger after the procedure is finished, this is a sign that the chlorine disinfection has not been effective enough and should be repeated. Before repeating the procedures, it is important to flush the distribution system. This will remove the substances dissolved by chlorine, and new chlorine rich water can easily remove the remaining biofilm. 5. Emptying tanks and distribution system of chlorine rich water Empty the chlorinated potable water tank, and flush the distribution system with water from another tank, by opening all taps. Take random samples to document chlorine content below 0.5 mg/l after flushing. 6. Special treatment of shower heads and shower hoses Plastic shower heads and shower hoses are often difficult to chlorinate, as they may contain much biofilm. Every three months such fixtures should be disassembled, cleaned (mechanically or by using soap) before they are disinfected. Disinfection may be done by soaking them in 50 mg/l free chlorine for an hour, by boiling them in water until they have an internal temperature of 100 o C, or by hanging them until they are completely dry internally. If the procedures described above do not give low colony counts, the reason for this must be found.

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Append ix 13 – Cleani ng and disinf ection of potable water tanks Below is one possible method for cleaning and disinfection of potable water tanks. 1. Preparation The storage capacity in all other potable water tanks should be fully utilized. If re-coating of the tank is required, it will take up to one week before the tank may be ready for use, provided that the hardening process does not cause any problems. If problems arise, the tank may be out of operation for a long time. The amount of water needed, hardening requirements, manpower, potable water production possibilities etc. should be considered and included in planning the maintenance work, to ensure enough water during the maintenance period. 2. Drainage The tank should be drained completely. If necessary, a mobile drain pump should be used. 3. Inspection/supervision The frequency of cleaning/disinfection should be assessed during tank inspection/supervision. With a small amount of slime and sediment in the tank and with low and stable colony counts, the cleaning intervals are satisfactory. The inspection results shall be logged. 4. Cleaning For cleaning purposes, only use water of potable water quality. The surfaces in the tank should be flushed under high pressure, and better results may be achieved through use of certified cleaning agents, see 2.3.4. If necessary, the surface may have to be scrubbed with stiff brushes. After the scrubbing and flushing, the tanks should be completely drained. 5. Inspection/supervision After draining the tank should be inspected to evaluate the cleaning. The protective coating shall be assessed and completely or partly renewed if necessary. The air-vent opening, including float ball and corrosion proof net, shall be checked and repaired if necessary. The inspection results shall be logged. 6. Appliance of protective coating The protective coating has to be certified and applied according to the recommendations made by the manufacturer, since application of the protective coating and/or insufficient hardening has caused problems on many offshore installations, see 9.1.4. A log should document that this work has been done correctly with regard to method of application, hardening, washing and thickness of coating. The next monthly potable water analysis should include hydrocarbons, and the values should not have increased significantly since the previous yearly potable water test. 7. Disinfection Water that in addition to tank disinfection, is intended for disinfection of the distribution system, must hold a chlorine content of approximately 5 mg/l chlorine (5ppm). If the water is not intended for disinfection of the distribution system, a chlorine content of at least 10 mg/l (ppm) is recommended. A suggested calculation method for the chlorine solution can be found in appendix 11 . When the storage tank has been completely filled up, the water shall have a free chlorine content of at least 4 mg/l (ppm). The water should not be used for at least 12 hours, but it should preferably be circulated in the tank. 8. Control After 12 hours a sample should be taken to document that the water still contains enough free chlorine; the chlorine reduction should be less than 1 mg/l. Normally the tank water is dumped, as it does not satisfy the potable water requirements regarding smell and taste. On the other hand, the water can be used for disinfection of the distribution system, provided that the free chlorine content is approximately 5 mg per litre, see appendix 12.

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Water Bunkering on Platforms

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